一定要加上这句话才能ac

if(a[0] == q) return 1;

#include <iostream>
using namespace std;

const int N = 1e6 + 1;
int a[N];

int find_index(int q, int n){
    int l = 0, r = n - 1;
    if(a[0] == q) return 1;
	while (l + 1 != r){
		int mid = (l + r) / 2;
		if (a[mid] >= q) r = mid;
		else l = mid;
	}
	
	if (a[r] == q) return r + 1; 
	else return -1;
}

int main(){
    int n, m;
    scanf("%d %d", &n, &m);
    for(int i = 0; i < n; ++i) scanf("%d", &a[i]);
    while(m --){
        int q;
        scanf("%d", &q);
        printf("%d ", find_index(q, n));
    }
    return 0;
}