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跟天下第一挺像的
1 void Bellman(int v0) 2 { 3 int i, k; 4 for (int i = 0; i < n; ++i) { 5 dist[i] = INF, path[i] = -1; 6 } 7 dist[v0] = 0; 8 for (k = 1; k < n; ++k) { 9 for (i = 0; i < m; ++i) { 10 if (dist[edges[i].u] != INF && edges[i].w + dist[edges[i].u] < dist[edges[i].v]) { 11 dist[edges[i].v] = edges[i].w + dist[edges[i].u]; 12 path[edges[i].v] = edges[i].u; 13 } 14 } 15 } 16 } 17 18 //判断是否存在从原点可达的负权值回路 19 for (i = 0; i < m; ++i) { 20 if (dist[edges[i].u] != INF && edges[i].w + dist[edges[i].u] < dist[edges[i].v]) 21 return 0; 22 } 23 return 1;
该算法还可以求最长路径
Bellman-Ford 判断环 + 最大路径值是否大于1
1 #include<iostream> 2 #include<cstdio> 3 #include<cstdlib> 4 #include<cstring> 5 #include<string> 6 #include<queue> 7 #include<algorithm> 8 #include<map> 9 #include<iomanip> 10 #include<climits> 11 #include<string.h> 12 #include<cmath> 13 #include<stdlib.h> 14 #include<vector> 15 #include<set> 16 #define INF 1e7 17 #define MAXN 100010 18 #define maxn 50 19 #define maxm 1000 20 #define Mod 1000007 21 using namespace std; 22 typedef long long LL; 23 24 struct exchange{ 25 int ci, cj; 26 double cij; 27 }ex[maxm]; 28 int i, j, k; 29 int n, m; 30 string name[maxn], a, b; 31 double x, maxdist[maxn]; 32 bool flag; 33 int kase = 0; 34 35 int readkase() 36 { 37 cin >> n; 38 if (n == 0) return 0; 39 for (i = 0; i < n; ++i) 40 cin >> name[i]; 41 cin >> m; 42 for (i = 0; i < m; ++i) { 43 cin >> a >> x >> b; 44 for (j = 0; a != name[j]; ++j); 45 for (k = 0; b != name[k]; ++k); 46 ex[i].ci = j, ex[i].cj = k, ex[i].cij = x; 47 } 48 return 1; 49 } 50 51 void Bellman(int v0) 52 { 53 flag = false; 54 memset(maxdist,0,sizeof(maxdist)); 55 maxdist[v0] = 1; 56 for (k = 1; k <= n; ++k) { //从maxdist(0)递推到maxdist(n) 57 for (i = 0; i < m; ++i) {//判断加入每条边是否能是最大距离增大 58 if (maxdist[ex[i].ci] * ex[i].cij > maxdist[ex[i].cj]) 59 maxdist[ex[i].cj] = maxdist[ex[i].ci] * ex[i].cij; 60 } 61 } 62 if (maxdist[v0] > 1.0) flag = true; 63 } 64 65 int main() 66 { 67 while (readkase()) { 68 for (int i = 0; i < n; ++i) { 69 Bellman(i); 70 if (flag) break; 71 } 72 if (flag) printf("Case %d: Yes\n",++kase); 73 else printf("Case %d: No\n", ++kase); 74 } 75 return 0; 76 }
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原文地址：http://www.cnblogs.com/usedrosee/p/4337795.html
