Single Element in a Sorted Array

Posted 2020-09-28 amazingzoe

Given a sorted array consisting of only integers where every element appears twice except for one element which appears once. Find this single element that appears only once.

Example 1:

Input: [1,1,2,3,3,4,4,8,8]
Output: 2

 

Example 2:

Input: [3,3,7,7,10,11,11]
Output: 10

 

Note: Your solution should run in O(log n) time and O(1) space.

 

 1 public class Solution {
 2     public int singleNonDuplicate(int[] nums) {
 3         int left = 0, right = nums.length - 1;
 4         
 5         while (left <= right) {
 6             if (left == right) return nums[left];
 7             
 8             int mid = left + (right - left) / 2;
 9             if (mid > 0 && mid < right && nums[mid] != nums[mid - 1] && nums[mid] != nums[mid + 1])
10                 return nums[mid];
11             
12             if (mid > 0 & nums[mid - 1] == nums[mid]) {
13                 if ((mid - left) % 2 == 1) left = mid + 1;
14                 else right = mid - 2;
15             } else if (mid <= right && nums[mid] == nums[mid + 1]) {
16                 if ((mid - left) % 2 == 1) right = mid - 1;
17                 else left = mid + 2;
18             }
19         }
20         return -1;
21     }
22 }