README_EN.md

540. Single Element in a Sorted Array

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Description

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

 

Constraints:

• 1 <= nums.length <= 105
• 0 <= nums[i] <= 105

Solutions

Binary search.

Python3

class Solution:
    def singleNonDuplicate(self, nums: List[int]) -> int:
        left, right = 0, len(nums) - 1
        while left < right:
            mid = (left + right) >> 1
            # Equals to: if (mid % 2 == 0 and nums[mid] != nums[mid + 1]) or (mid % 2 == 1 and nums[mid] != nums[mid - 1]):
            if nums[mid] != nums[mid ^ 1]:
                right = mid
            else:
                left = mid + 1
        return nums[left]

Java

class Solution {
    public int singleNonDuplicate(int[] nums) {
        int left = 0, right = nums.length - 1;
        while (left < right) {
            int mid = (left + right) >> 1;
            // if ((mid % 2 == 0 && nums[mid] != nums[mid + 1]) || (mid % 2 == 1 && nums[mid] != nums[mid - 1])) {
            if (nums[mid] != nums[mid ^ 1]) {
                right = mid;
            } else {
                left = mid + 1;
            }
        }
        return nums[left];
    }
}

TypeScript

function singleNonDuplicate(nums: number[]): number {
    let left = 0,
        right = nums.length - 1;
    while (left < right) {
        const mid = (left + right) >> 1;
        if (nums[mid] != nums[mid ^ 1]) {
            right = mid;
        } else {
            left = mid + 1;
        }
    }
    return nums[left];
}

C++

class Solution {
public:
    int singleNonDuplicate(vector<int>& nums) {
        int left = 0, right = nums.size() - 1;
        while (left < right)
        {
            int mid = left + right >> 1;
            if (nums[mid] != nums[mid ^ 1]) right = mid;
            else left = mid + 1;
        }
        return nums[left];
    }
};

Go

func singleNonDuplicate(nums []int) int {
	left, right := 0, len(nums)-1
	for left < right {
		mid := (left + right) >> 1
		if nums[mid] != nums[mid^1] {
			right = mid
		} else {
			left = mid + 1
		}
	}
	return nums[left]
}

Rust

impl Solution {
    pub fn single_non_duplicate(nums: Vec<i32>) -> i32 {
        let mut l = 0;
        let mut r = nums.len() - 1;
        while l < r {
            let mid = l + r >> 1;
            if nums[mid] == nums[mid ^ 1] {
                l = mid + 1;
            } else {
                r = mid;
            }
        }
        nums[l]
    }
}

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