UVA - 10986 Sending email 最短路的spfa算法

来源：互联网发布：银行家算法安全性算法编辑：程序博客网时间：2024/05/20 04:13

题目大意：有n个服务器，m条线将其连接起来了，要求将信息从s服务器送到t服务器，求最短的时间，如果送不到的话，另外输出

解题思路：这题的数量比较大，用邻接矩阵的话会暴，所以用邻接表来表示，具体思路不变

#include<cstdio>#include<cstring>#include<algorithm>#include<queue>using namespace std;#define maxn 100005#define INF 0x3f3f3f3fint n,m,s,t;int head[maxn],next[maxn],u[maxn],v[maxn],w[maxn],d[maxn];int vis[maxn];void init() {scanf("%d%d%d%d",&n,&m,&s,&t);memset(head,-1,sizeof(head));for(int e = 1; e <= m; e++) {scanf("%d%d%d",&u[e],&v[e],&w[e]);u[e+m] = v[e];v[e+m] = u[e];w[e+m] = w[e];next[e] = head[u[e]];head[u[e]] = e;next[e+m] = head[u[e+m]];head[u[e+m]] = e+m;}}void spfa(int scr) {memset(vis,0,sizeof(vis));for(int i = 0; i < n; i++)d[i] = INF;queue<int> q;d[scr] = 0;q.push(scr);int temp ;while(!q.empty()){temp = q.front();q.pop();vis[temp] = 0;for(int e = head[temp]; e != -1; e= next[e])if(d[temp] + w[e] < d[v[e]]) {d[v[e]] = d[temp] + w[e];if(!vis[v[e]]) {vis[v[e]] = 1;q.push(v[e]);}}}}int main() {int test,mark = 1;scanf("%d",&test);while(test--) {init();spfa(s);if(d[t] != INF)printf("Case #%d: %d\n",mark++,d[t]);elseprintf("Case #%d: unreachable\n",mark++);}return 0;}

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