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;
}
};