折半查找

/**
 * Performs the standard binary search
 * @return index where item is found, or -1 if not found.
 */
public static <AnyType extends Comparable<? super AnyType>> int binarySearch(AnyType[] a, AnyType x){

	int low = 0, hign = a.length-1;
	while(low<=high){
		int mid = (low+high)/2;
		if(a[mid].compareTo(x) < 0){
			low = mid+1;
		}else if(a[mid].compareTo(x) > 0){
			high = mid -1;
		}else{
			return mid;   //Found
		}
	}
	return NOT_FOUND;	//NOT_FOUND is defined as -1;
}