Leetcode 33 Search in Rotated Sorted Array 二分查找变式

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.

在循环错位的有序数组中找出特定元素。

二分的一个变式，分情况讨论一下，详见注释。

class Solution {public:    int search(vector<int>& nums, int target)     {        int l=0,r=nums.size()-1;        while(l<=r)        {            int mid=(r+l)/2;            if(nums[mid]==target)                 return mid;            if(nums[mid]>=nums[l]) //mid在左侧大一些的区间            {                if(nums[l]<=target && nums[mid]>target) //target比mid小，但大于l，向左移                    r=mid-1;                else                    l=mid+1;            }            else //mid在右侧小一些的区间            {                if(nums[r]>=target && nums[mid]<target)//target比mid大，但小于r，向右移                    l=mid+1;                else                    r=mid-1;            }        }        return -1;    }};