二分搜索法

public class BinarySearch {
	
	public static int binarySearch(int[] a,int x){
		int low=0;
		int high=a.length -1;
		int mid;
		while(low<=high){
			mid=(low+high)/2;
			if(a[mid]<x){
				low=mid+1;
			}else if(mid>x){
				high=mid-1;
			}else
				return mid;
		}
		return -1;
	}
}