二分查找

复杂度 O(lgN)

使用条件：数据已经排序并在内存中。

package chapter1;

public class BinarySearch <T>{
	
	public static <T extends Comparable<? super T>> int binarySearch(T [] a, T x){
		int low =0; 
		int high = 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;
			}
		}
		return -1; //not found
		
	}

}