33 Search in Rotated Sorted Array

33. Search in Rotated Sorted Array

1. Question

Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.

(i.e.,0 1 2 4 5 6 7might become4 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.

2. Implementation

(1) Binary Search

class Solution {
    public int search(int[] nums, int target) {
        if (nums == null || nums.length == 0) {
            return -1;
        }

        int start = 0, end = nums.length - 1, mid = 0;

        while (start + 1 < end) {
            mid = start + (end - start) / 2;

            if (nums[mid] == target) {
                return mid;
            }
            else if (nums[mid] < nums[end]) {
                if (nums[mid] < target && target <= nums[end]) {
                    start = mid + 1;
                }
                else {
                    end = mid - 1;
                }
            }
            else {
                if (nums[start] <= target && target < nums[mid]) {
                    end = mid - 1;
                }
                else {
                    start = mid + 1;
                }
            }
        }

        if (nums[start] == target) {
            return start;
        }
        else if (nums[end] == target) {
            return end;
        }
        else {
            return -1;
        }
    }
}

3. Time & Space Complexity

时间复杂度O(logn), 空间复杂度O(1)