#include 
     
      #include 
      
       #include 
       
        using namespace std;int binSearch(int A[], int length, int key){	int L = 0, R = length - 1;	while (L <= R){		int M = (L + R) / 2;		if (A[M]>key)			R = M-1;		else if (A[M] < key)			L = M+1;		else			//return M;若不做处理，在有重复值的情况下，返回下标不一定为第一个。		{			if (A[M - 1] == key)			{				R = R - 1;			}			else{				return M;			}		}	}	return -1;}void main(){	int A[] = { 0, 1, 2, 3, 4, 4,5,5};	cout << binSearch(A, 7,4);}