Help me in solving CNDY problem

help
,
1

My issue

find out runtime error

My code

#include <stdio.h>
#include <stdbool.h>
#define MAX_A 1000
int main() {
    int s, a, b[2 * MAX_A], count[MAX_A];
    bool isValid;
    scanf("%d", &s);
    while (s--) {
        scanf("%d", &a);
        for (int i = 0; i < 2 * a; i++) {
            scanf("%d", &b[i]);
        }
        for (int i = 0; i < MAX_A; i++) {
            count[i] = 0;
        }
        for (int i = 0; i < 2 * a; i++) {
            count[b[i]]++;
        }
        isValid = true;
        for (int i = 0; i < MAX_A; i++) {
            if (count[i] > 2) {
                isValid = false;
                break;
            }
        }
        if (isValid) {
            printf("Yes\n");
        } else {
            printf("No\n");
        }
    }
    return 0;
}

Learning course: Roadmap to 3*
Problem Link: https://www.codechef.com/learn/course/klu-roadmap-3star/KLURMP300A/problems/CNDY