CF1153D Pigeon d'Or

Description

给一棵树，每个点是子节点的最大值或最小值，将叶子节点填上整数，使这棵树的根最大。

Solution

明显的(dp)题，代码很短。
分类讨论如下：

1、如果是叶子节点，(d_x = 1)

2、如果是(min)节点，(d_x =sum_{y in son_x} d_y)

3、如果是(max)节点，(d_x = min_{y in son_x} d_y)

#include <bits/stdc++.h>
using namespace std;
const int N = 300005;
int n, a[N], b[N], x, k, ans[N], c[N];
int main() {
    scanf("%d", &n);
    for (int i = 1; i <= n; i++) {
        scanf("%d", &a[i]);
        ans[i] = a[i] ? n + 1 : 0, c[i] = -1;
    }
    for (int i = 2; i <= n; i++) {
        scanf("%d", &x);
        b[i] = x, c[x] = i;
    }
    for (int i = n; i > 1; i--) {
        if (c[i] == -1)
            ans[i] = 1, k++;
        x = b[i];
        ans[x] = a[x] ? std::min(ans[x], ans[i]) : ans[x] + ans[i];
    }
    printf("%d
", k + 1 - ans[1]);
    return 0;
}