算法----二分查找算法

public class Demo {
	public static void main(String[] args){
		int[] num = {1,2,3,4};
		int index = 3;
		int start = 0;
		int end = num.length-1;
		boolean flag = false;
		if(index>=num[0]&&index<=num[end]){
			while(index<=num[end]){
				int middle = (start + end)/2;
				if(index==num[middle]){
					System.out.println(middle);
					flag = true;
					break;
				}
				if(index<num[middle]){
					end = middle-1;
				}
				if(index>num[middle]){
					start = middle+1;
				}
			}
		}
		if(flag==false){
			System.out.println("没有找到");
		}
		
	}
}