Single Number

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

You may view the full question here.

Approach 1: Here is an approach using HashMaps —

//Approach 1:
//Runtime: 7ms
//Memory usage: 38.6MB
class Solution {
    public int singleNumber(int[] nums) {
        HashMap<Integer, Integer> map = new HashMap();
        for(int n : nums){
            if(map.containsKey(n)){
                map.remove(n);
            } else {
                map.put(n, 1);
            }
        }
        for(int key : map.keySet()){
            return key;
        }
        return 0;
    }
    
}

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Cheers & Chao!