LeetCode Link: 33. Search in Rotated Sorted Array
Language: C#
Problem Statement
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.
Examples
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
Solution
public class Solution
{
public int Search(int[] nums, int target)
{
var pivot = GetPivot(nums);
if (target > nums[nums.Length - 1])
{
return BinarySearch(nums, target, 0, pivot - 1);
}
return BinarySearch(nums, target, pivot, nums.Length);
}
private int BinarySearch(int[] nums, int target, int l, int h)
{
while (l <= h)
{
var mid = (l + h) / 2;
if (nums[mid] == target)
{
return mid;
}
if (nums[mid] > target)
{
h = mid - 1;
}
else
{
l = mid + 1;
}
}
return -1;
}
private int GetPivot(int[] nums)
{
var left = 0;
var right = nums.Length - 1;
if (nums[0] < nums[right])
{
return 0;
}
while (left <= right)
{
var mid = (left + right) / 2;
if (mid > 0 && nums[mid] < nums[mid - 1] )
{
return mid;
}
if (mid < nums.Length - 1 && nums[mid] > nums[mid + 1])
{
return mid + 1;
}
if (nums[left] > nums[mid])
{
right = mid - 1;
}
else
{
left = mid + 1;
}
}
return 0;
}
}
Complexity
Time Complexity: O(logN)
Space Complexity: O(1)