Java数组-二分查找原理

二分查找又叫做折半查找

前提：数组必须是有序的

思想：每次都猜想中间的那个元素，当或大或小时候就能排除掉一般的元素

画图帮助理解一下

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代码：

public class LookInTwo {
	public static void main(String[] args) {
		int[] arr = {12,34,23,41,15,65,2,4};
		int[] arr2=BubbleDemo.getBubble(arr);
		for(int i=0;i<arr2.length;i++){
			if (i==0) {
				System.out.print("["+arr2[i]+" ");
			}else if (i==arr2.length-1) {
				System.out.print(arr2[arr2.length-1]+"]");
			}else {
				System.out.print(arr2[i]+" ");
			}
		}
		System.out.println();
		System.out.println(getLookInTwo(arr2, 41));
	}
	public static int getLookInTwo(int[] arr,int num){
		int start = 0;
		int end = arr.length;
		while(start<=end){
			int mid =(start+end)/2;
			if(arr[mid]==num){
				return mid;
			}else if(arr[mid]>num){
				end=mid-1;
			}else{
				start = mid+1;
			}
		}
		return -1;
	}
	
}