33. Search in Rotated Sorted Array

• Difficulty: Medium

• Topics: Array, Binary Search

• Similar Questions:

  • Search in Rotated Sorted Array II

  • Find Minimum in Rotated Sorted Array

Problem:

Suppose an array sorted in ascending order 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.

Your algorithm's runtime complexity must be in the order of O(log n).

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

Solutions:

class Solution {
public:
    /**
     * @param A: an integer rotated sorted array
     * @param target: an integer to be searched
     * @return: an integer
     */
    int search(vector<int> &A, int target) {
        // write your code here
        if (A.size() == 0)  return -1;
        int left = 0;
        int right = A.size() - 1;
        while (left + 1 < right) {
            int mid = left + ((right - left) >> 1);
            if (A[mid] == target)  return mid;
            if (A[left] < A[right]) {
                if (A[mid] < target) {
                    left = mid;
                } else {
                    right = mid;
                }
            } else {
                if (A[mid] > A[left]) {
                    if (A[mid] > target && A[left] <= target) {
                        right = mid;
                    } else {
                        left = mid;
                    }
                } else {
                    if (A[mid] < target && A[right] >= target) {
                        left = mid;
                    } else {
                        right = mid;
                    }
                }
            }
        }


        if (A[left] == target)  return left;
        if (A[right] == target) return right;
        return -1;
    }
};