C. Alyona and the Tree

 

http://codeforces.com/contest/682/problem/C

 

dfs，没什么好说的，直接看代码吧

 

import java.util.ArrayList;
import java.util.Scanner;


public class Main {
    static long[] a = new long[(int) (1e5 + 50)];
    static ArrayList<Edge>[] al = new ArrayList[(int) (1e5 + 50)];

    public static void main(String[] args) {
        Scanner io = new Scanner(System.in);
        int n = io.nextInt();
        for (int i = 1; i <= n; i++) a[i] = io.nextInt();
        for (int i = 0; i < al.length; i++) al[i] = new ArrayList<>();
        for (int x = 2, y, len; x <= n; x++) {
            y = io.nextInt();
            len = io.nextInt();
            al[y].add(new Edge(x, len));
        }
        dfs(1, Long.MIN_VALUE/2);
        System.out.println(ans);
    }


    static int ans = 0;

    static void dfs(int x, long max) {
        if (max > a[x]) {
            ans += child(x);
            return;
        }

        for (Edge e : al[x]) dfs(e.y, Math.max(e.len, max + e.len));
    }

    static int child(int x) {
        int size = 1;
        for (Edge e : al[x]) size += child(e.y);
        return size;
    }

    static class Edge {
        int y, len;

        public Edge(int y, int len) {
            this.y = y;
            this.len = len;
        }
    }
}