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# 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 = 
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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