单选题 以下二分查找算法是( )的. int binarySearch(int a[],int x){ //a 中的元素递增有序 int n=a.length; int low=0,high=n-1; while(low+1!=high) int mid=(low+high)/2; if(x>=a_mid])low=mid; else high=mid; if(x==a[low])return low; else return -1; }