题解

#include <stdio.h>
int main()
{
    int n;
    scanf("%d",&n);
    int a[n];
    for (int i=0;i<n;i++)
    {
        scanf("%d",&a[i]);
    }
    int l=0,r=n-1,x;
    scanf("%d",&x);
    while (l <= r)
    {
        int mid = l + r >> 1;
        if (a[mid] == x)
        {
            printf("%d",mid+1);
            return 0;
        }
        else if (a[mid] < x)
        {
            l = mid + 1;
        }
        else if (a[mid] > x)
        {
            r = mid - 1;
        }
    }
    printf("-1");
    return 0;
}