网易2018校招笔试题-游历魔法王国-只能过60%-如何优化

#include <iostream>
#include <vector>
#include <stack>
#include <algorithm>
#include <set>
#include <map>
#include <queue>
#include <unordered_map>
#include <cstdio>
using namespace std;

int F2(/*unordered_*/map<int, set<int>>&p, int left, int n, unordered_map<int,int>&mp, int city) {
	int ans = 0;
	ans = max(ans, (int)mp.size());
	if (left) {
		auto &ns = p[city];
		for (auto i:ns) {
			mp[i]++;
			ans = max(ans, F2(p, left - 1, n, mp, i));
			mp[i]--;
			if (mp[i] == 0) mp.erase(i);
		}
	}
	return ans;
}

int main() {
	int n, L;
	scanf("%d%d",&n,&L);
	/*unordered_*/map<int, set<int>> p;
	int i = 0, j = 0;
	for (i = 0; i < n-1; i++) {
		scanf("%d", &j);
		p[i + 1].insert(j);
		p[j].insert(i+1);
	}
	unordered_map<int, int>mp;
	mp[0]++;
	printf("%d\n",F2(p, L, n,mp,0));
	return 0;
}