hihocoder1224

来源：互联网发布：les蝴蝶电影知乎编辑：程序博客网时间：2024/06/06 00:53

#include <cstdio>#include <iostream>#include <algorithm>#include <queue>#include <stack>#include <cstring>#include <vector>using namespace std;vector<int> vec[100005];int d[100005];int dfs(int u){    int si = vec[u].size();    if(si == 0){        return d[u] = 0;    }    int ma = 0;    for(int i = 0;i < si;i++){        int v = vec[u][i];        ma= max(ma,dfs(v));    }    return d[u] = ma + 1;}void del(int u){    int si = vec[u].size();    for(int i = 0;i < si;i++){        int v = vec[u][i];        if(d[v] == d[u] - 1){            vec[u].clear();            del(v);            return;        }    }}int main(){    int n;    cin >> n;    for(int i = 1;i < n;i++){        int x,y;        scanf("%d%d",&x,&y);        vec[x].push_back(y);    }    dfs(1);    int ans = d[1];    del(1);    int ma = 0;    for(int i = 0;i < n;i++){        if(vec[i].size() != 0){            if(d[i] > ma){                ma = d[i];            }        }    }    if(ma == 0){        ma = -1;    }    cout <<ans+ma+1<< endl;    return 0;}

首先求出来一条最长路。然后求出除掉最长路之后最长路就可以了！

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