【dfs找不在简单路径的点】ZOJ 10th Anniversary Contest C ZOJ 3583

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int g[111][111];bool vis[111];bool visit[111];int pre[111];int n,m,s,t;void dfs(int u){    int i;    if(u==t || vis[u]){        while(u!=s){            vis[u] = 1;            u = pre[u];        }        return ;    }    for(i=0;i<n;i++){        if(g[u][i] && !visit[i]){            pre[i] = u;            visit[i] = 1;            dfs(i);            visit[i] = 0;        }    }}int main(){    while(scanf("%d%d%d%d",&n,&m,&s,&t) !=-1){        int i,j;        memset(g,0,sizeof(g));        while(m--){            int x,y;            scanf("%d%d",&x,&y);            g[x][y] = g[y][x] = 1;        }        for(i=0;i<n;i++){            vis[i] = 0;            pre[i] = -1;            visit[i] = 0;        }        visit[s] = 1;        dfs(s);        vis[s] = vis[t] = 1;        int ans = 0;        for(i=0;i<n;i++){            if(!vis[i])ans++;        }        printf("%d\n",ans);    }    return 0;}