Single Number

Description

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

Note:

Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

Example 1:

Input: [2,2,1]

Output: 1

Example 2:

Input: [4,1,2,1,2]

Output: 4

Code

Java

class Solution {
    public int singleNumber(int[] nums) {
        HashMap<Integer, Integer> hm = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            if (hm.containsKey(nums[i])) {
                hm.put(nums[i], hm.get(nums[i]) + 1);
            } else {
                hm.put(nums[i], 1);
            }
        }
        List<Map.Entry<Integer, Integer>> list = new ArrayList(hm.entrySet());
        list.sort(Comparator.comparingInt(Map.Entry::getValue));
        return list.get(0).getKey();
        
    }
}

XOR

class Solution {
    public int singleNumber(int[] nums) {
        int result = 0;
        for (int i = 0; i < nums.length; i++) {
            result ^= nums[i];
        }
        return result;
    }
}