Leetcode•Apr 20, 2026
Single Element in a Sorted Array
Hazrat Ali
Leetcode
You are given a sorted array consisting of only integers where every element appears exactly twice, except for one element which appears exactly once.
Return the single element that appears only once.
Your solution must run in O(log n) time and O(1) space.
Example 1:
Input: nums = [1,1,2,3,3,4,4,8,8] Output: 2
Example 2:
Input: nums = [3,3,7,7,10,11,11] Output: 10
Solution
var singleNonDuplicate = function(nums) {
let left = 0;
let right = nums.length - 1;
while (left < right) {
let mid = Math.floor((left + right) / 2);
if (mid % 2 === 1) mid--;
if (nums[mid] === nums[mid + 1]) {
left = mid + 2;
} else {
right = mid;
}
}
return nums[left];
};