Single Number LeetCode Solution

Problem – Single Number

Given a non-empty array of integers nums, every element appears twice except for one. Find that single one.

You must implement a solution with a linear runtime complexity and use only constant extra space.

Example 1:

Input: nums = [2,2,1]
Output: 1

Example 2:

Input: nums = [4,1,2,1,2]
Output: 4

Example 3:

Input: nums = [1]
Output: 1

Constraints:

• 1 <= nums.length <= 3 * 104
• -3 * 104 <= nums[i] <= 3 * 104
• Each element in the array appears twice except for one element which appears only once.

Single Number LeetCode Solution in C++

class Solution {
public:
    int singleNumber(vector<int>& nums) { 
       unordered_map<int,int> a;
	   for(auto x: nums)
		   a[x]++;
	   for(auto z:a)
		   if(z.second==1)
			   return z.first;
	   return -1;
    }
};

Single Number LeetCode Solution in Python

class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        xor = 0
        for num in nums:
            xor ^= num
        
        return xor

Single Number LeetCode Solution in Java

public int singleNumber(int[] nums) {
    int ans =0;
    
    int len = nums.length;
    for(int i=0;i!=len;i++)
        ans ^= nums[i];
    
    return ans;
    
}

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