Bellman_ford最短路

 1 #include <cstdio>
 2 #include <iostream>
 3 #include <algorithm>
 4 #include <cstring>
 5 #include <cmath>
 6 #include <queue>
 7 #define inf 0x3f3f3f3f
 8 const int maxn = 200;
 9 int n, m, pre[maxn], edge[maxn * maxn][3];
10 int dist[maxn];
11 bool relax(int u, int v, int c){
12     if(dist[v] > dist[u] + c){
13         dist[v] = dist[u] + c; pre[v] = u;
14         return true;
15     }
16     return  false;
17 }
18 int bellman(int S){
19     int i, j;
20     for(i = 0; i < n; i ++){
21         dist[i] = inf;
22         pre[i] = -1;
23     }
24     dist[S] = 0;
25     bool flag;
26     for(i = 1;i < n; i ++){
27         flag = false;
28         for(j = 0; j < m; j ++)
29             if(relax(edge[j][0], edge[j][1], edge[j][2])) flag = true;
30         if(!flag) break;
31     }
32     for(j = 0; j < m; j ++)
33         if(relax(edge[j][0], edge[j][1], edge[j][2])) return false;
34     return true;
35 }