136. Single Number

LeetCode

class Solution {
    public int singleNumber(int[] nums) {
        Map<Integer,Integer> map=new HashMap<>();
        for(int num:nums){
            map.put(num,map.getOrDefault(num,0)+1);
        }
        for(Map.Entry<Integer,Integer> entry:map.entrySet()){
            if(entry.getValue()==1) return entry.getKey();
        }
        return -1;
    }
}

Bit Manipulation

class Solution {
  public int singleNumber(int[] nums) {
    int a = 0;
    for (int i : nums) {
      a ^= i;
    }
    return a;
  }
}