[LeetCode]Search in Rotated Sorted Array

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;
    }
};