Is there an efficient solution to the travelling salesman problem with binary edge weights?












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Is there a way to solve TSP in polynomial time if there are only two kinds of weights, 0 and 1?










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    Is there a way to solve TSP in polynomial time if there are only two kinds of weights, 0 and 1?










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      3


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      $begingroup$


      Is there a way to solve TSP in polynomial time if there are only two kinds of weights, 0 and 1?










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      WiccanKarnak is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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      Is there a way to solve TSP in polynomial time if there are only two kinds of weights, 0 and 1?







      traveling-salesman






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      edited yesterday









      Apass.Jack

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      asked yesterday









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          2 Answers
          2






          active

          oldest

          votes


















          7












          $begingroup$

          No, since if every edge has weight 1, there is still the question of whether any such tour exists, which is the Hamiltonian Cycle problem, and this is still NP-hard. (The link is to a Wikipedia page for Hamiltonian Path -- both the path and cycle versions of the problem are hard.)






          share|cite|improve this answer









          $endgroup$









          • 3




            $begingroup$
            I initially read the question with the assumption it's asking about complete graphs - but then you can still get the Hamiltonian Cycle problem by asking if a zero-length Hamiltonian cycle exists. And if you allow retrace, the problem becomes trivial.
            $endgroup$
            – John Dvorak
            yesterday












          • $begingroup$
            @JohnDvorak thanks a lot, is there a way if I guarantee no Hamiltonian Cycles?
            $endgroup$
            – WiccanKarnak
            yesterday










          • $begingroup$
            Every complete graph has a Hamiltonian cycle. And if your graph doesn't have a Hamiltonian cycle ... then it definitely doesn't have a Hamiltonian cycle, so what was the question again?
            $endgroup$
            – John Dvorak
            yesterday












          • $begingroup$
            @WiccanKarnak : (A TSP solution is a Hamiltonian cycle ... of minimal total weight.)
            $endgroup$
            – Eric Towers
            yesterday










          • $begingroup$
            Aren't you allowed to use the same edge twice in TSP?
            $endgroup$
            – immibis
            yesterday



















          2












          $begingroup$

          The accepted answer isn't quite right. An instance of TSP consists of a distance between every pair of cities: that is, it consists of a weighted complete graph. Every complete graph has a Hamiltonian cycle.



          However, it is simple to reduce HAMILTON-CYCLE to $0$$1$ TSP. Given a graph $G$, create a TSP instance where the cities are the vertices and the distance is $0$ if there is an edge between the cities and $1$ if there is not. Then $G$ has a Hamiltonian cyle if, and only if, the TSP instance has a tour of weight zero. Therefore, $0$$1$ TSP is NP-complete.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            This is a good point, though the choice of whether to require the input graph to be complete or not never makes a practical difference (for the purpose of finding a distance-minimal tour, missing edges in a graph can be encoded as arbitrarily-distant edges in a complete graph). Interestingly, in looking for a definitively canonical definition of the TSP problem, I found that on p. 211 of Garey & Johnson (1979) they require the edge weights to be in $mathbb Z^+$ -- i.e., 0-length edges are forbidden, meaning that for them, the "0-1 TSP" described here is technically not a special case of TSP!
            $endgroup$
            – j_random_hacker
            16 hours ago










          • $begingroup$
            @j_random_hacker It's a good job I'm only throwing small stones in my glass house! (Actually, you can reduce $0$-$1$ TSP to $1$-$2$ TSP by just adding one to every edge weight and adding $n$ to the length of the path you're looking for.)
            $endgroup$
            – David Richerby
            16 hours ago













          Your Answer





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          2 Answers
          2






          active

          oldest

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          2 Answers
          2






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

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          7












          $begingroup$

          No, since if every edge has weight 1, there is still the question of whether any such tour exists, which is the Hamiltonian Cycle problem, and this is still NP-hard. (The link is to a Wikipedia page for Hamiltonian Path -- both the path and cycle versions of the problem are hard.)






          share|cite|improve this answer









          $endgroup$









          • 3




            $begingroup$
            I initially read the question with the assumption it's asking about complete graphs - but then you can still get the Hamiltonian Cycle problem by asking if a zero-length Hamiltonian cycle exists. And if you allow retrace, the problem becomes trivial.
            $endgroup$
            – John Dvorak
            yesterday












          • $begingroup$
            @JohnDvorak thanks a lot, is there a way if I guarantee no Hamiltonian Cycles?
            $endgroup$
            – WiccanKarnak
            yesterday










          • $begingroup$
            Every complete graph has a Hamiltonian cycle. And if your graph doesn't have a Hamiltonian cycle ... then it definitely doesn't have a Hamiltonian cycle, so what was the question again?
            $endgroup$
            – John Dvorak
            yesterday












          • $begingroup$
            @WiccanKarnak : (A TSP solution is a Hamiltonian cycle ... of minimal total weight.)
            $endgroup$
            – Eric Towers
            yesterday










          • $begingroup$
            Aren't you allowed to use the same edge twice in TSP?
            $endgroup$
            – immibis
            yesterday
















          7












          $begingroup$

          No, since if every edge has weight 1, there is still the question of whether any such tour exists, which is the Hamiltonian Cycle problem, and this is still NP-hard. (The link is to a Wikipedia page for Hamiltonian Path -- both the path and cycle versions of the problem are hard.)






          share|cite|improve this answer









          $endgroup$









          • 3




            $begingroup$
            I initially read the question with the assumption it's asking about complete graphs - but then you can still get the Hamiltonian Cycle problem by asking if a zero-length Hamiltonian cycle exists. And if you allow retrace, the problem becomes trivial.
            $endgroup$
            – John Dvorak
            yesterday












          • $begingroup$
            @JohnDvorak thanks a lot, is there a way if I guarantee no Hamiltonian Cycles?
            $endgroup$
            – WiccanKarnak
            yesterday










          • $begingroup$
            Every complete graph has a Hamiltonian cycle. And if your graph doesn't have a Hamiltonian cycle ... then it definitely doesn't have a Hamiltonian cycle, so what was the question again?
            $endgroup$
            – John Dvorak
            yesterday












          • $begingroup$
            @WiccanKarnak : (A TSP solution is a Hamiltonian cycle ... of minimal total weight.)
            $endgroup$
            – Eric Towers
            yesterday










          • $begingroup$
            Aren't you allowed to use the same edge twice in TSP?
            $endgroup$
            – immibis
            yesterday














          7












          7








          7





          $begingroup$

          No, since if every edge has weight 1, there is still the question of whether any such tour exists, which is the Hamiltonian Cycle problem, and this is still NP-hard. (The link is to a Wikipedia page for Hamiltonian Path -- both the path and cycle versions of the problem are hard.)






          share|cite|improve this answer









          $endgroup$



          No, since if every edge has weight 1, there is still the question of whether any such tour exists, which is the Hamiltonian Cycle problem, and this is still NP-hard. (The link is to a Wikipedia page for Hamiltonian Path -- both the path and cycle versions of the problem are hard.)







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered yesterday









          j_random_hackerj_random_hacker

          2,91211016




          2,91211016








          • 3




            $begingroup$
            I initially read the question with the assumption it's asking about complete graphs - but then you can still get the Hamiltonian Cycle problem by asking if a zero-length Hamiltonian cycle exists. And if you allow retrace, the problem becomes trivial.
            $endgroup$
            – John Dvorak
            yesterday












          • $begingroup$
            @JohnDvorak thanks a lot, is there a way if I guarantee no Hamiltonian Cycles?
            $endgroup$
            – WiccanKarnak
            yesterday










          • $begingroup$
            Every complete graph has a Hamiltonian cycle. And if your graph doesn't have a Hamiltonian cycle ... then it definitely doesn't have a Hamiltonian cycle, so what was the question again?
            $endgroup$
            – John Dvorak
            yesterday












          • $begingroup$
            @WiccanKarnak : (A TSP solution is a Hamiltonian cycle ... of minimal total weight.)
            $endgroup$
            – Eric Towers
            yesterday










          • $begingroup$
            Aren't you allowed to use the same edge twice in TSP?
            $endgroup$
            – immibis
            yesterday














          • 3




            $begingroup$
            I initially read the question with the assumption it's asking about complete graphs - but then you can still get the Hamiltonian Cycle problem by asking if a zero-length Hamiltonian cycle exists. And if you allow retrace, the problem becomes trivial.
            $endgroup$
            – John Dvorak
            yesterday












          • $begingroup$
            @JohnDvorak thanks a lot, is there a way if I guarantee no Hamiltonian Cycles?
            $endgroup$
            – WiccanKarnak
            yesterday










          • $begingroup$
            Every complete graph has a Hamiltonian cycle. And if your graph doesn't have a Hamiltonian cycle ... then it definitely doesn't have a Hamiltonian cycle, so what was the question again?
            $endgroup$
            – John Dvorak
            yesterday












          • $begingroup$
            @WiccanKarnak : (A TSP solution is a Hamiltonian cycle ... of minimal total weight.)
            $endgroup$
            – Eric Towers
            yesterday










          • $begingroup$
            Aren't you allowed to use the same edge twice in TSP?
            $endgroup$
            – immibis
            yesterday








          3




          3




          $begingroup$
          I initially read the question with the assumption it's asking about complete graphs - but then you can still get the Hamiltonian Cycle problem by asking if a zero-length Hamiltonian cycle exists. And if you allow retrace, the problem becomes trivial.
          $endgroup$
          – John Dvorak
          yesterday






          $begingroup$
          I initially read the question with the assumption it's asking about complete graphs - but then you can still get the Hamiltonian Cycle problem by asking if a zero-length Hamiltonian cycle exists. And if you allow retrace, the problem becomes trivial.
          $endgroup$
          – John Dvorak
          yesterday














          $begingroup$
          @JohnDvorak thanks a lot, is there a way if I guarantee no Hamiltonian Cycles?
          $endgroup$
          – WiccanKarnak
          yesterday




          $begingroup$
          @JohnDvorak thanks a lot, is there a way if I guarantee no Hamiltonian Cycles?
          $endgroup$
          – WiccanKarnak
          yesterday












          $begingroup$
          Every complete graph has a Hamiltonian cycle. And if your graph doesn't have a Hamiltonian cycle ... then it definitely doesn't have a Hamiltonian cycle, so what was the question again?
          $endgroup$
          – John Dvorak
          yesterday






          $begingroup$
          Every complete graph has a Hamiltonian cycle. And if your graph doesn't have a Hamiltonian cycle ... then it definitely doesn't have a Hamiltonian cycle, so what was the question again?
          $endgroup$
          – John Dvorak
          yesterday














          $begingroup$
          @WiccanKarnak : (A TSP solution is a Hamiltonian cycle ... of minimal total weight.)
          $endgroup$
          – Eric Towers
          yesterday




          $begingroup$
          @WiccanKarnak : (A TSP solution is a Hamiltonian cycle ... of minimal total weight.)
          $endgroup$
          – Eric Towers
          yesterday












          $begingroup$
          Aren't you allowed to use the same edge twice in TSP?
          $endgroup$
          – immibis
          yesterday




          $begingroup$
          Aren't you allowed to use the same edge twice in TSP?
          $endgroup$
          – immibis
          yesterday











          2












          $begingroup$

          The accepted answer isn't quite right. An instance of TSP consists of a distance between every pair of cities: that is, it consists of a weighted complete graph. Every complete graph has a Hamiltonian cycle.



          However, it is simple to reduce HAMILTON-CYCLE to $0$$1$ TSP. Given a graph $G$, create a TSP instance where the cities are the vertices and the distance is $0$ if there is an edge between the cities and $1$ if there is not. Then $G$ has a Hamiltonian cyle if, and only if, the TSP instance has a tour of weight zero. Therefore, $0$$1$ TSP is NP-complete.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            This is a good point, though the choice of whether to require the input graph to be complete or not never makes a practical difference (for the purpose of finding a distance-minimal tour, missing edges in a graph can be encoded as arbitrarily-distant edges in a complete graph). Interestingly, in looking for a definitively canonical definition of the TSP problem, I found that on p. 211 of Garey & Johnson (1979) they require the edge weights to be in $mathbb Z^+$ -- i.e., 0-length edges are forbidden, meaning that for them, the "0-1 TSP" described here is technically not a special case of TSP!
            $endgroup$
            – j_random_hacker
            16 hours ago










          • $begingroup$
            @j_random_hacker It's a good job I'm only throwing small stones in my glass house! (Actually, you can reduce $0$-$1$ TSP to $1$-$2$ TSP by just adding one to every edge weight and adding $n$ to the length of the path you're looking for.)
            $endgroup$
            – David Richerby
            16 hours ago


















          2












          $begingroup$

          The accepted answer isn't quite right. An instance of TSP consists of a distance between every pair of cities: that is, it consists of a weighted complete graph. Every complete graph has a Hamiltonian cycle.



          However, it is simple to reduce HAMILTON-CYCLE to $0$$1$ TSP. Given a graph $G$, create a TSP instance where the cities are the vertices and the distance is $0$ if there is an edge between the cities and $1$ if there is not. Then $G$ has a Hamiltonian cyle if, and only if, the TSP instance has a tour of weight zero. Therefore, $0$$1$ TSP is NP-complete.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            This is a good point, though the choice of whether to require the input graph to be complete or not never makes a practical difference (for the purpose of finding a distance-minimal tour, missing edges in a graph can be encoded as arbitrarily-distant edges in a complete graph). Interestingly, in looking for a definitively canonical definition of the TSP problem, I found that on p. 211 of Garey & Johnson (1979) they require the edge weights to be in $mathbb Z^+$ -- i.e., 0-length edges are forbidden, meaning that for them, the "0-1 TSP" described here is technically not a special case of TSP!
            $endgroup$
            – j_random_hacker
            16 hours ago










          • $begingroup$
            @j_random_hacker It's a good job I'm only throwing small stones in my glass house! (Actually, you can reduce $0$-$1$ TSP to $1$-$2$ TSP by just adding one to every edge weight and adding $n$ to the length of the path you're looking for.)
            $endgroup$
            – David Richerby
            16 hours ago
















          2












          2








          2





          $begingroup$

          The accepted answer isn't quite right. An instance of TSP consists of a distance between every pair of cities: that is, it consists of a weighted complete graph. Every complete graph has a Hamiltonian cycle.



          However, it is simple to reduce HAMILTON-CYCLE to $0$$1$ TSP. Given a graph $G$, create a TSP instance where the cities are the vertices and the distance is $0$ if there is an edge between the cities and $1$ if there is not. Then $G$ has a Hamiltonian cyle if, and only if, the TSP instance has a tour of weight zero. Therefore, $0$$1$ TSP is NP-complete.






          share|cite|improve this answer









          $endgroup$



          The accepted answer isn't quite right. An instance of TSP consists of a distance between every pair of cities: that is, it consists of a weighted complete graph. Every complete graph has a Hamiltonian cycle.



          However, it is simple to reduce HAMILTON-CYCLE to $0$$1$ TSP. Given a graph $G$, create a TSP instance where the cities are the vertices and the distance is $0$ if there is an edge between the cities and $1$ if there is not. Then $G$ has a Hamiltonian cyle if, and only if, the TSP instance has a tour of weight zero. Therefore, $0$$1$ TSP is NP-complete.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered yesterday









          David RicherbyDavid Richerby

          69.1k15106195




          69.1k15106195












          • $begingroup$
            This is a good point, though the choice of whether to require the input graph to be complete or not never makes a practical difference (for the purpose of finding a distance-minimal tour, missing edges in a graph can be encoded as arbitrarily-distant edges in a complete graph). Interestingly, in looking for a definitively canonical definition of the TSP problem, I found that on p. 211 of Garey & Johnson (1979) they require the edge weights to be in $mathbb Z^+$ -- i.e., 0-length edges are forbidden, meaning that for them, the "0-1 TSP" described here is technically not a special case of TSP!
            $endgroup$
            – j_random_hacker
            16 hours ago










          • $begingroup$
            @j_random_hacker It's a good job I'm only throwing small stones in my glass house! (Actually, you can reduce $0$-$1$ TSP to $1$-$2$ TSP by just adding one to every edge weight and adding $n$ to the length of the path you're looking for.)
            $endgroup$
            – David Richerby
            16 hours ago




















          • $begingroup$
            This is a good point, though the choice of whether to require the input graph to be complete or not never makes a practical difference (for the purpose of finding a distance-minimal tour, missing edges in a graph can be encoded as arbitrarily-distant edges in a complete graph). Interestingly, in looking for a definitively canonical definition of the TSP problem, I found that on p. 211 of Garey & Johnson (1979) they require the edge weights to be in $mathbb Z^+$ -- i.e., 0-length edges are forbidden, meaning that for them, the "0-1 TSP" described here is technically not a special case of TSP!
            $endgroup$
            – j_random_hacker
            16 hours ago










          • $begingroup$
            @j_random_hacker It's a good job I'm only throwing small stones in my glass house! (Actually, you can reduce $0$-$1$ TSP to $1$-$2$ TSP by just adding one to every edge weight and adding $n$ to the length of the path you're looking for.)
            $endgroup$
            – David Richerby
            16 hours ago


















          $begingroup$
          This is a good point, though the choice of whether to require the input graph to be complete or not never makes a practical difference (for the purpose of finding a distance-minimal tour, missing edges in a graph can be encoded as arbitrarily-distant edges in a complete graph). Interestingly, in looking for a definitively canonical definition of the TSP problem, I found that on p. 211 of Garey & Johnson (1979) they require the edge weights to be in $mathbb Z^+$ -- i.e., 0-length edges are forbidden, meaning that for them, the "0-1 TSP" described here is technically not a special case of TSP!
          $endgroup$
          – j_random_hacker
          16 hours ago




          $begingroup$
          This is a good point, though the choice of whether to require the input graph to be complete or not never makes a practical difference (for the purpose of finding a distance-minimal tour, missing edges in a graph can be encoded as arbitrarily-distant edges in a complete graph). Interestingly, in looking for a definitively canonical definition of the TSP problem, I found that on p. 211 of Garey & Johnson (1979) they require the edge weights to be in $mathbb Z^+$ -- i.e., 0-length edges are forbidden, meaning that for them, the "0-1 TSP" described here is technically not a special case of TSP!
          $endgroup$
          – j_random_hacker
          16 hours ago












          $begingroup$
          @j_random_hacker It's a good job I'm only throwing small stones in my glass house! (Actually, you can reduce $0$-$1$ TSP to $1$-$2$ TSP by just adding one to every edge weight and adding $n$ to the length of the path you're looking for.)
          $endgroup$
          – David Richerby
          16 hours ago






          $begingroup$
          @j_random_hacker It's a good job I'm only throwing small stones in my glass house! (Actually, you can reduce $0$-$1$ TSP to $1$-$2$ TSP by just adding one to every edge weight and adding $n$ to the length of the path you're looking for.)
          $endgroup$
          – David Richerby
          16 hours ago












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