【个人算法模板】无根树转有根树

代码实现

/*
p数组：用来存放节点i的父节点
root：用来指定根节点是哪个
*/
#include<bits/stdc++.h>
using namespace std;
const int maxn = 2e5+10;
int p[maxn];
vector<int> g[maxn];
void dfs(int u,int fa){
    int s = g[u].size();
    for(int i = 0; i < s; i++){
        int v = g[u][i];
        if(v!=fa) dfs(v,p[v]=u);
    }
}
int main(void){
    int n;
    cin >> n;
    for(int i = 1; i < n; i++){
        int u,v;
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    int root = 1;
    p[root] = -1;
    dfs(root,-1);
    for(int i = 0; i < n; i++){
        if(i==root) cout<<"root is "<<i<<" father is "<<p[i]<<endl;
        else{
            cout<<"The father of "<<i<<" is "<<p[i]<<endl;
        }
    }
    return 0;
}