数组的二分查找 

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package xianxingbiao;

public class BiSearch {
//数组的二分查找
	public static void main(String[] args) {
		// TODO Auto-generated method stub

		int [] arr=new int[] {1,2,3,4,5,6,7,8,9};//数组必须有序
		
		int high=arr.length-1;
		int low=0;
		int mid=(low+high)/2;
		int ele=9;//查找元素
		int tag=-1;//目标元素的位置
		
		while(low<=high) {
			if(ele==arr[mid]) {
				tag=mid;
				break;
			}else if(ele<arr[mid]) {
				high=mid-1;
				mid=(low+high)/2;
			}else {
				low=mid+1;
				mid=(low+high)/2;
			}
		}
		
		System.out.println(tag);
	}
}

注意：
1、二分查找只能对有序数组查找;
2、时间复杂度：O(log2(n));