旅游规划--信息学一本通

bfs第一次写崩了，超时到怀疑人生

 

 

 

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<vector>
#include<queue>
#define maxn 200010
using namespace std;
vector<int>G[maxn];
void insert(int be, int en) {
    G[be].push_back(en);
}
int n;
int dis1[maxn];
int dis2[maxn];
int vis[maxn];
 
int dfs1(int x, int fa, int dp) {//求直径
    dis1[x] = dp;
    for (int i = 0; i < G[x].size(); i++) {
        int p = G[x][i];
        if (p == fa) continue;
         
        dfs1(p, x, dp + 1);
    }
    return 0;
}
 
int bfs(int be,int *dis) {                  //标记层数
    queue<int>que;
    que.push(be);
    dis1[be] = -1;
    while (!que.empty()) {
        int x = que.front();
        que.pop();
        for (int i = 0; i < G[x].size(); i++) {
            int p = G[x][i];
            if (!vis[p]) {
                vis[p] = 1;
                dis[p] = dis[x] + 1;
                que.push(p);
            }
        }
    }
    return 0;
}
int dfs(int x,int fa) {
    for (int i = 0; i < G[x].size(); i++) {
        int p = G[x][i];
        if (p == fa) continue;
        if (dis1[p] > dis1[x]) {
            dfs(p, x);
            dis2[x] = max(dis2[x], dis2[p] + 1);
        }
    }
    return 0;
}
int main() {
    int be, en;
    scanf("%d", &n);
    for (int i = 1; i < n; i++) {
        scanf("%d %d", &be, &en);
        insert(be, en);
        insert(en, be);
    }
    dfs1(1, -1, 0);
    int s=0, t=0;
    int len = 0;
    for (int i = 0; i < n; i++) {
        if (dis1[s] < dis1[i]) {
            s = i;
            len = dis1[i];
        }
    }
    memset(dis1, 0, sizeof(dis1));
    dfs1(s, -1, 0);
    for (int i = 0; i < n; i++) {
        len = max(dis1[i], len);            //获得直径
    }
 
    for (int i = 0; i < n; i++) {            //把一端直径捆起来
        if (dis1[i] == len) {
            insert(n, i);
            insert(i, n);
        }
    }
    bfs(n, dis1);
    for (int i = 0; i < n; i++) {
        if (dis1[i] == len) {
            insert(n + 1, i);
            insert(i, n + 1);
        }
    }
    memset(vis, 0, sizeof(vis));
    bfs(n + 1, dis2);
    for (int i = 0; i < n; i++) {
        if (dis1[i] + dis2[i] == len + 1) {
            printf("%d\n", i);
        }
    }
    return 0;
}

　　

来源：https://www.cnblogs.com/lesning/p/11735353.html