二分查找（两种）

柔情只为你懂 2023-10-03 15:24 7阅读 0赞

在二分查找中，有一个关键点，就是关于传入方法当中的数组长度是否-1，其影响在代码编写过程中的边界问题

1.数组长度 - 1

public static int binarySearch(int[] array,int n){
            int left = 0;
            int right = array.length - 1;
            while(left <= right){
                int mid = (left + right) / 2;
                if (array[mid] == n){
                    return mid;
                }else if (array[mid] < n){
                    left = mid + 1;
                }else{
                    right = mid - 1;
                }
            }
            return -1;
        }
     public static void main(String[] args) {
            int[] arr = {1,2,3,4,5,6,7,8,9};
            int ret = binarySearch(arr,5);
            System.out.println(ret);
        }

运行结果：

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAb2hhbmHvvIE_size_19_color_FFFFFF_t_70_g_se_x_16][]

2.数组长度不 - 1

public static int binarySearch2(int[] array,int n){
            int left = 0;
            int right = array.length;
            while(left < right){
                int mid = (left + right) / 2;
                if (array[mid] == n){
                    return mid;
                }else if (array[mid] < n){
                    left = mid + 1;
                }else{
                    right = mid;
                }
            }
            return -1;
        }
        public static void main(String[] args) {
            int[] arr = {1,2,3,4,5,6,7,8,9};
            int ret = binarySearch2(arr,1);
            System.out.println(ret);
        }

运行结果：

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAb2hhbmHvvIE_size_20_color_FFFFFF_t_70_g_se_x_16][]

[watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAb2hhbmHvvIE_size_19_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/20210828161804789.png?x-oss-process=image/watermark,type_ZHJvaWRzYW5zZmFsbGJhY2s,shadow_50,text_Q1NETiBAb2hhbmHvvIE=,size_19,color_FFFFFF,t_70,g_se,x_16
[watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAb2hhbmHvvIE_size_20_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/20210828162905790.png?x-oss-process=image/watermark,type_ZHJvaWRzYW5zZmFsbGJhY2s,shadow_50,text_Q1NETiBAb2hhbmHvvIE=,size_20,color_FFFFFF,t_70,g_se,x_16