LeetCode 33. Search in Rotated Sorted Array

题目描述:

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.

首先找到有序序列平移了多少位, 然后根据target在哪个范围内使用二分搜索.

class Solution {
public:
    int search(vector<int>& nums, int target) {
        if(nums.empty()) return -1;
        int start = 0, end = nums.size();
        for(int i = 0; i < nums.size() - 1; i++){
            if(nums[i] > nums[i + 1]){
                start = i + 1;
                break;
            }
        }
        if(target < nums[0]){
            return binSearch(nums, start, nums.size(), target);
        }
        else{
            return binSearch(nums, 0, start ? start : nums.size(), target);
        }
    }
    
    int binSearch(vector<int> &nums, int left, int right, int target){
        int low = left, high = right, mid = (low + high) / 2;
        while(low < high){
            if(nums[mid] == target)
                return mid;
            else if(nums[mid] > target)
                high = mid;
            else
                low = mid + 1;
            
            mid = (low + high) / 2;
        }
        return -1;
    }
};