二分查找（两种）

Posted 2021-09-13 ohana！

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：

 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：