代码

#include <algorithm>
#include <map> 

using namespace std;

int binary_search(const unsigned *a, int n, unsigned x)
{
    static map <unsigned, int> num = {{~0, n}};
    if (num.count(x))
        return num[x];
	return num[x] = lower_bound(a + num.lower_bound(x) -> second, a + num.upper_bound(x) -> second, x) - a;
}

评测结果