求树的重心

给定一棵树,求树的重心的编号以及重心删除后得到的最大子树的节点个数size,如果size相同就选取编号最小的.

首先要知道什么是树的重心,树的重心定义为:找到一个点,其所有的子树中最大的子树节点数最少,那么这个点就是这棵树的重心,删去重

心后，生成的多棵树尽可能平衡

 

 

 

 

 

#include <iostream>
#include <algorithm>
#include <string>
#include <string.h>
#include <vector>
#include <map>
#include <stack>
#include <set>
#include <queue>
#include <math.h>
#include <cstdio>
#include <iomanip>
#include <time.h>
#include <bitset>
#include <cmath>

#define LL long long
#define INF 0x3f3f3f3f
#define ls nod<<1
#define rs (nod<<1)+1

const double eps = 1e-10;
const int maxn = 2e4 + 10;
const LL mod = 1e9 + 7;

int sgn(double a){return a < -eps ? -1 : a < eps ? 0 : 1;}
using namespace std;

vector<int> vec[maxn];
int siz[maxn],dep[maxn],mx[maxn];
int ans = maxn,id = maxn,cnt,n;

void get_size(int x,int f) {
    siz[x] = 1;
    for (int i = 0;i < vec[x].size();i++) {
        int v = vec[x][i];
        if (v == f)
            continue;
        get_size(vec[x][i],x);
        siz[x] += siz[vec[x][i]];
        cnt = max(cnt,siz[v]);
    }
    mx[x] = max(cnt,n-siz[x]);
}

void get_dep(int x) {
    for (int i = 0;i < vec[x].size();i++) {
        dep[vec[x][i]] = dep[x] + 1;
        get_dep(vec[x][i]);
    }
}

//void get_val(int x) {
//    val[x] = w[x];
//    for (int i = 0;i < vec[i].size();i++) {
//        get_val(vec[x][i]);
//        val[x] = max(val[x],val[vec[x][i]]);
//    }
//}

int main() {
    int T;
    scanf("%d",&T);
    while (T--) {
        ans = maxn,id = maxn,cnt = 0;
        memset(siz,0, sizeof(siz));
        memset(mx,0, sizeof(mx));
        for (int i = 0;i < maxn;i++)
            vec[i].clear();
        scanf("%d",&n);
        for (int i = 1;i <= n-1;i++) {
            int u,v;
            scanf("%d%d",&u,&v);
            vec[u].push_back(v);
            vec[v].push_back(u);
        }
        get_size(1,0);
        for (int i = 1;i <= n;i++) {
            if (mx[i] < ans) {
                ans = mx[i];
                id = i;
            }
        }
        printf("%d %d\n",id,ans);
    }
    return 0;
}