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.Numerics;
using System.Linq;
using System.Text;
using static System.Math;

class MainClass
{

    public static void Main(string[] args)
    {
        var _ = LnInts();
        var N = _[0]; var M = _[1];
        var H = LnInts();
        var towers = new Tower[N];
        for(int i = 0; i < N; i++)
        {
            towers[i] = new Tower();
            towers[i].h = H[i];
        }
        for(int i = 0; i < M; i++)
        {
            var con = LnInts();
            towers[con[0] - 1].connect.Add(con[1] - 1);
            towers[con[1] - 1].connect.Add(con[0] - 1);
        }
        int goods = 0;
        for(int i = 0; i < N; i++)
        {
            bool good = true;
            foreach(var n in towers[i].connect)
            {
                if (towers[i].h <= towers[n].h) { good = false; }
            }
           if(good) goods++;
        }
        print(goods);
    }

    public class Tower
    {
        public long h;
        public HashSet<int> connect=new HashSet<int>();
    }

    public static void print(object obj) { Console.WriteLine(obj); }
    public static long Gcd(long a, long b) { if (a > b) { var r = a % b; if (r == 0) return b; else return Gcd(b, r); } else { var r = b % a; if (r == 0) return a; else return Gcd(a, r); } }
    public static int Gcd(int a, int b) { if (a > b) { var r = a % b; if (r == 0) return b; else return Gcd(b, r); } else { var r = b % a; if (r == 0) return a; else return Gcd(a, r); } }
    public static int[] LnInts() { var vs = Console.ReadLine().Trim().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries); var ins = new int[vs.Length]; for (int i = 0; i < vs.Length; i++) ins[i] = int.Parse(vs[i]); return ins; }
    public static int LnInt() { var vs = Console.ReadLine().Trim(); return int.Parse(vs); }
    public static long[] LnLngs() { var vs = Console.ReadLine().Trim().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries); var ins = new long[vs.Length]; for (int i = 0; i < vs.Length; i++) ins[i] = long.Parse(vs[i]); return ins; }
    public static long LnLng() { var vs = Console.ReadLine().Trim(); return long.Parse(vs); }
    public static string[] LnStrs() { var vs = Console.ReadLine().Trim().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries); return vs; }
    public static string LnStr() { var vs = Console.ReadLine().Trim(); return vs; }
public static List<T[]> AllPermutation<T>(params T[] array) where T : IComparable{var a = new List<T>(array).ToArray();var res = new List<T[]>();res.Add(new List<T>(a).ToArray());var n = a.Length;var next = true;while (next){next = false;int i;for (i = n - 2; i >= 0; i--){if (a[i].CompareTo(a[i + 1]) < 0) break;}if (i < 0) break;var j = n;do{j--;} while (a[i].CompareTo(a[j]) > 0);if (a[i].CompareTo(a[j]) < 0){var tmp = a[i];a[i] = a[j];a[j] = tmp;Array.Reverse(a, i + 1, n - i - 1);res.Add(new List<T>(a).ToArray());next = true;}}return res;}}