Problem:
Score : 300 points

Problem Statement

There are N observatories in AtCoder Hill, called Obs. 1, Obs. 2, ..., Obs. N. The elevation of Obs. i is H_i.
There are also M roads, each connecting two different observatories. Road j connects Obs. A_j and Obs. B_j.

Obs. i is said to be good when its elevation is higher than those of all observatories that can be reached from Obs. i using just one road.
Note that Obs. i is also good when no observatory can be reached from Obs. i using just one road.

How many good observatories are there?

Constraints

2 \leq N \leq 10^5

1 \leq M \leq 10^5

1 \leq H_i \leq 10^9

1 \leq A_i,B_i \leq N

A_i \neq B_i

Multiple roads may connect the same pair of observatories.

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N M
H_1 H_2 ... H_N
A_1 B_1
A_2 B_2
:
A_M B_M

Output

Print the number of good observatories.

Sample Input 1

4 3
1 2 3 4
1 3
2 3
2 4

Sample Output 1

2

From Obs. 1, you can reach Obs. 3 using just one road. The elevation of Obs. 1 is not higher than that of Obs. 3, so Obs. 1 is not good.

From Obs. 2, you can reach Obs. 3 and 4 using just one road. The elevation of Obs. 2 is not higher than that of Obs. 3, so Obs. 2 is not good.

From Obs. 3, you can reach Obs. 1 and 2 using just one road. The elevation of Obs. 3 is higher than those of Obs. 1 and 2, so Obs. 3 is good.

From Obs. 4, you can reach Obs. 2 using just one road. The elevation of Obs. 4 is higher than that of Obs. 2, so Obs. 4 is good.

Thus, the good observatories are Obs. 3 and 4, so there are two good observatories.

Sample Input 2

6 5
8 6 9 1 2 1
1 3
4 2
4 3
4 6
4 6

Sample Output 2

3

Solution in C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        var inputs = Console.ReadLine().Split(' ').Select(long.Parse).ToArray();
        var n = inputs[0];
        var m = inputs[1];

        var h = Console.ReadLine().Split(' ').Select(long.Parse).ToArray();

        Dictionary<long, List<long>> Towers = new Dictionary<long, List<long>>();

        for (int i = 0; i < n; i++) Towers[i] = new List<long>();

        for(int i = 0; i < m; i++)
        {
            var ab = Console.ReadLine().Split(' ').Select(long.Parse).ToArray();

            Towers[ab[0] - 1].Add(ab[1]);
            Towers[ab[1] - 1].Add(ab[0]);
        }

        // 一個もないもの
        long ans = Towers.Where(t => t.Value.Count == 0).Count();

        // 一番高い
        var tmp = Towers.Where(t => t.Value.Count != 0).ToArray();
        foreach(var item in tmp)
        {
            bool flag = true;

            foreach(var tour in item.Value)
            {
                if (h[item.Key] <= h[tour - 1]) flag = false;
            }

            if (flag) ans++;
        }

        Console.WriteLine(ans);
    }
}