K - Kingdom’s Power

比赛的时候思路出了 但不会证。

赛后敲了就过了。

#include <bits/stdc++.h>
using namespace std;

const int N = 1000010;
#define ll long long
int n;

vector <pair<int, int>> tr[N];
int depth[N];
int val[N];

int dfs1(int u, int dep) {
    if(tr[u].empty()) return 1;

    depth[u] = dep;
    for(auto &x : tr[u])
        x.first = dfs1(x.second, dep+1);

    sort(tr[u].begin(), tr[u].end());
    return tr[u].back().first + 1;
}

int dfs2(int u, int Val) {
    val[u] = Val;
    if(tr[u].empty()) return 1;

    int minl = Val;
    for(auto &x : tr[u]) {
        minl = min(depth[u], dfs2(x.second, minl+1));
    }
    return minl + 1;
}

int main() {
    int t;
    int fa;
    scanf("%d", &t);
    for(int Case = 1;Case <= t;Case ++) {
        scanf("%d", &n);
        for(int i = 1;i <= n;i ++) tr[i].clear();
        for(int i = 2;i <= n;i ++) {
            scanf("%d", &fa);
            tr[fa].push_back(make_pair(0, i));
        }
        dfs1(1, 0);
        dfs2(1, 0);
		ll ans=0;
		for(int i=1;i<=n;i++)
			if(tr[i].empty())
				ans+=val[i];

        printf("Case #%d: %d\n", Case, ans);
    }
}