ans

check()函数用于判断a[mid]是否等于x

如果大于等于 r=mid

否则 l=mid

以下是代码

#include <bits/stdc++.h>
using namespace std;
int n;
int a[1000010];
int x;
bool check(int y) {
    if (y >= x)
        return 1;
    return 0;
}
int bs() {
    int l = 0, r = n;
    while (l + 1 < r) {
        int mid = (l + r) / 2;
        if (check(a[mid]))
            r = mid;
        else
            l = mid;
    }
    if (a[l] == x)
        return l;
    if (a[r] == x)
        return r;
    return -1;
}
int main() {
    scanf("%d", &n);
    for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
    scanf("%d", &x);
    printf("%d", bs());
    return 0;
}