HIHO #1050 : 树中的最长路 （dfs 树的直径）

题目链接
树的直径的计算：任选一点dfs到最远点p，然后从p在dfs到最远点的距离就是树的直径

#include<cstdio>#include<algorithm>#include<iostream>#include<cstring>#include<string>#include<cmath>#include<queue>#include<map>#include<set>#include<cstdlib>#include<vector>using namespace std;#define cl(a,b) memset(a,b,sizeof(a))#define LL long long#define pb push_back#define gcd __gcd#define For(i,j,k) for(int i=(j);i<k;i++)#define lowbit(i) (i&(-i))#define _(x) printf("%d\n",x)const int maxn = 3e6+10;const int inf  = 1 << 28;int n;vector<int> G[maxn];int tmp;int sum;void dfs(int u,int fa,int dis){    if(sum<dis){        sum = dis;        tmp = u;    }    for(int i=0;i<G[u].size();i++){        int v = G[u][i];        if(v==fa)continue;        dfs(v,u,dis+1);    }}int main(){    scanf("%d",&n);    for(int i=0;i<n-1;i++){        int x,y;scanf("%d%d",&x,&y);        G[x].pb(y);G[y].pb(x);    }    sum=0;    dfs(1,-1,0);//cout<<"tmp "<<tmp<<" sum "<<sum<<endl;    sum = 0;    dfs(tmp,-1,0);    printf("%d\n",sum);    return 0;}