最短路-SPAF模板

以hdu1874畅通工程续为例

 #include<iostream>
 #include<cstring>
 #include<cstdio>
 #include<queue>
 using namespace std;
 const int maxn = ;
 vector<pair<int, int> > E[maxn];
 int d[maxn], inq[maxn];
 int n, m,s,t;
 
 void SPFA(int s)
 {
     queue<int> Q;
     Q.push(s); d[s] = , inq[s] = ;
     while (!Q.empty())
     {
         int now = Q.front(); Q.pop();
         inq[now] = ;
         for (int i = ; i < E[now].size(); i++) {
             int v = E[now][i].first;
             if (d[v] > d[now] + E[now][i].second)
             {
                 d[v] = d[now] + E[now][i].second;
                 if (inq[v] == ) continue;
                 inq[v] = ;
                 Q.push(v);
             }
         }
     }
 }
 
 int main()
 {
     while (scanf("%d%d",&n,&m)==)
     {
         for (int i = ; i < maxn; i++) {
             E[i].clear(); inq[i] = , d[i] = 1e9;
         }
         for (int i = ; i < m; i++) {
             int x, y, z;
             scanf("%d%d%d", &x, &y, &z);
             E[x].push_back(make_pair(y, z));
             E[y].push_back(make_pair(x, z));
         }
         scanf("%d%d", &s, &t);
         SPFA(s);
         if (d[t] == 1e9)
             printf("-1\n");
         else
             printf("%d\n", d[t]);
     }
     return ;
 }