search_in_sorted_rotated_array.cpp

/*
    There is an integer array nums sorted in ascending order (with distinct values).

    Prior to being passed to your function, nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k], nums[k+1], ..., nums[n-1], nums[0], nums[1], ..., nums[k-1]] (0-indexed). For example, [0,1,2,4,5,6,7] might be rotated at pivot index 3 and become [4,5,6,7,0,1,2].

    Given the array nums after the possible rotation and an integer target, return the index of target if it is in nums, or -1 if it is not in nums.

    You must write an algorithm with O(log n) runtime complexity.

    Example 1:
    Input: nums = [4,5,6,7,0,1,2], target = 0
    Output: 4

    Example 2:
    Input: nums = [4,5,6,7,0,1,2], target = 3
    Output: -1

    Example 3:
    Input: nums = [1], target = 0
    Output: -1
    
    Constraints:
    1 <= nums.length <= 5000
    -104 <= nums[i] <= 104
    All values of nums are unique.
    nums is an ascending array that is possibly rotated.
    -104 <= target <= 104

*/

class Solution {
public:
    int search(vector<int>& nums, int target) {
        int start = 0, end = nums.size() - 1;
        int ans = -1;
        while(start <= end){
            int mid = start + (end - start) / 2;
            if(target == nums[mid]){
                return mid;
            }
            if(nums[start] <= nums[mid]){
                if(target >= nums[start] && target <= nums[mid]){
                    end = mid - 1;
                }
                else{
                    start = mid + 1;
                }
            }
            else{
                if(target >= nums[mid] && target <= nums[end]){
                    start = mid + 1;
                }
                else {
                    end = mid - 1;
                }
            }
        }
        return ans;
    }
};