思路

lower_bound() 包含algorithm头文件

a[i] : 1, 3, 5, 7, 9

pos = lower_bound(a, a + n, x) - a;
x = 0, pos = 0;
x = 1, pos = 1;
x = 9, pos = 4;
x = 10, pos = 5;
即lower_bound() return 第一个 >= 指定元素的位置

拓展

1. upper_bound() 更多…

#include <iostream>
#include <algorithm>

using namespace std;

const int N = 1e4 + 10;

int n, m;
int a[N];

int main()
{
    int cnt = 1;
    while(cin >> n >> m, n || m)
    {
        printf("CASE# %d:\n", cnt ++ );
        for(int i = 0; i < n; i ++ )
            cin >> a[i];
        sort(a, a + n);
        while(m -- )
        {
            int x;
            cin >> x;
            int pos = lower_bound(a, a + n, x) - a;
            if(a[pos] == x)
                printf("%d found at %d\n", x, pos + 1);
            else 
                printf("%d not found\n", x);
        }
    }
    return 0;
}