binary search

  //binary search 
public static int binarySearch(int[] a , int key){
	int lo=0, hi=a.length-1;
	while (lo<=hi){
		int mid = lo+(hi-lo)/2;
		if (key<a[mid]){
			hi=mid-1;
		}
		else if (key>a[mid]){
			lo=mid+1;
		}
		else return mid;
	}
	reture -1;
}