二分查找的错误写法

版权声明：嘿嘿嘿 https://blog.csdn.net/luzhensmart/article/details/87890988

public class W {

    public static void main(String[] args) {
        int[] a = {1,2,3,4,5,6,7,8,9};
        int b = midSearch(a,0,a.length-1,7);
        System.out.println(a[b]);
    }

    public static int midSearch(int a[],int start,int end,int target){

        while (start <= end){
            int mid = (start+end)/2;
            if(a[mid] == target){
                return mid;
            }else if(a[mid] < target){
                //第一次进来的时候 start=0 end=8
                //这里虽然递归调用了 但是里面返回的6 却给予了c 所以会继续递归死循环的执行
                int c = midSearch(a,mid+1,end,target);
                System.out.println(c);
            }else{
                midSearch(a,start,mid-1,target);
            }
        }
        return -1;
    }
}

打印结果：无线死循环 哈哈

应该改成：

public class W {

    public static void main(String[] args) {
        int[] a = {1,2,3,4,5,6,7,8,9};
        int b = midSearch(a,0,a.length-1,7);
        System.out.println(a[b]);
    }

    public static int midSearch(int a[],int start,int end,int target){

        while (start <= end){
            int mid = (start+end)/2;
            if(a[mid] == target){
                return mid;
            }else if(a[mid] < target){
               start = mid + 1;
            }else{
               end = mid - 1;
            }
        }
        return -1;
    }
}

 打印结果：