hdu 1595 find the longest of the shortest （spfa）

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记录最短路上的路径依次枚举删掉，看看剩下的最短路最大值是多少。

#include<stdio.h>#include<string.h>#include<algorithm>#include<queue>using namespace std;#define N 1005const int inf = 1 << 28;struct node{    int to, nxt, w;}e[N*N];int dis[N], vis[N];int head[N];int pre[N];int n, m;int cnt;int a[N][N];void init(){    memset(head, -1, sizeof(head));    memset(pre, 0, sizeof(pre));    memset(a, 0, sizeof(a));    cnt = 0;}void add( int u, int v, int w ){    e[cnt].to = v;    e[cnt].w = w;    e[cnt].nxt = head[u];    head[u] = cnt++;}void spfa(){queue<int> q;while( !q.empty() )q.pop();for( int i = 1; i <= n; i++ ){vis[i] = 0;dis[i] = inf;}vis[1] = 1;dis[1] = 0;q.push(1);while( !q.empty() ){int now = q.front();q.pop();vis[now] = 0;for( int i = head[now]; ~i; i = e[i].nxt ){int to = e[i].to;if( dis[to] > dis[now] + e[i].w ){dis[to] = dis[now] + e[i].w;pre[to] = now;if( !vis[to] ){vis[to] = 1;q.push(to);}}}}}void spfa1(){queue<int> q;while( !q.empty() )q.pop();for( int i = 1; i <= n; i++ ){vis[i] = 0;dis[i] = inf;}vis[1] = 1;dis[1] = 0;q.push(1);while( !q.empty() ){int now = q.front();q.pop();vis[now] = 0;for( int i = head[now]; ~i; i = e[i].nxt ){int to = e[i].to;if( a[now][to] && dis[to] > dis[now] + e[i].w ){dis[to] = dis[now] + e[i].w;//pre[to] = now;if( !vis[to] ){vis[to] = 1;q.push(to);}}}}}int main(){while(~scanf("%d%d", &n, &m)){init();int u, v, w;while(m--){scanf("%d%d%d", &u, &v, &w);add(u, v, w);add(v, u, w);a[u][v] = a[v][u] = 1;}int ans = 0;spfa();for( int i = n; i != 0; i = pre[i]){a[i][pre[i]] = a[pre[i]][i] = 0;spfa1();ans = max(ans, dis[n]);a[i][pre[i]] = a[pre[i]][i] = 1;}printf("%d\n", ans);}return 0;}

某处vis标记写错改了好久好久好久好久好久好久好久好久好久好久好久好久好久好久好久好久好久好久好久好久...

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