Leetcode Search in Rotated Sorted Array

Posted 2020-07-13 wuezs

题目链接：https://leetcode.com/problems/search-in-rotated-sorted-array/
题目：

Suppose a sorted array is rotated at some pivot unknown to you beforehand.

(i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2).

You are given a target value to search. If found in the array return its index, otherwise return -1.

You may assume no duplicate exists in the array.

思路：

 1、找到旋转点即第一个逆序，然后将数组分两半，分别用二分查找
 2、二分查找 根据左右跟中间比较的结果 对有序的部分采用二分查找。

算法：

public int search(int[] nums, int target) {  
    int left = 0,right = nums.length-1,mid = 0;  
    while(left<=right){  
        mid = left+(right-left)/2;  
        if(nums[mid]==target){  
            return mid;  
        }  
        if(nums[left]<nums[mid]){ //则left到mid有序  
            if(nums[left]==target){  
                return left;  
            }  
            if(nums[left]<=target&&target<nums[mid]){ //若target在left到mid之间  
                right = mid;  
            }else{  
                left = mid + 1;  
            }  
        }else{//则mid到right之间有序  
            if(target==nums[right]){  
                return right;  
            }  
            if(nums[mid]<target&&target<=nums[right]){ //若target在mid到right之间  
                left = mid + 1;  
            }else{  
                right = mid-1;  
            }  
        }  
    }  
    return -1;  
}