题目描述:(链接)
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.
解题思路:
二分查找,分三种情况讨论,找个例子,例如(0,1,2,3,4),把所有的旋转情况都画出来就可以了,主要是边界比较难确定。
class Solution { public: int search(vector<int>& nums, int target) { size_t first = 0; size_t last = nums.size(); while (first != last) { size_t mid = first + (last - first) / 2; if (nums[mid] == target) { return mid; } else if (nums[mid] >= nums[first]) { if (nums[first] <= target && target < nums[mid]) { last = mid; } else { first = mid + 1; } } else { if (nums[mid] < target && target <= nums[last - 1]) { first = mid + 1; } else { last = mid; } } } return -1; } };