LeetCode – Hashtable – Number of Good Pairs

Given an array of integers nums.

A pair (i,j) is called good if nums[i] == nums[j] and i < j.

Return the number of good pairs.

Example 1:

Input: nums = [1,2,3,1,1,3]
Output: 4
Explanation: There are 4 good pairs (0,3), (0,4), (3,4), (2,5) 0-indexed.

Example 2:

Input: nums = [1,1,1,1]
Output: 6
Explanation: Each pair in the array are good.

Example 3:

Input: nums = [1,2,3]
Output: 0

Constraints:

• 1 <= nums.length <= 100
• 1 <= nums[i] <= 100

class Solution {
    public int numIdenticalPairs(int[] nums) {
        Map<Integer,Integer> freqMap = new HashMap<Integer,Integer>();
        for(int i=0;i<nums.length;i++){
            freqMap.put(nums[i],freqMap.getOrDefault(nums[i],-1)+1);
        }
        int result = 0;
        for(int j:freqMap.values()){
            if(j!=0){
                int n = (j*(j+1))/2;
                result = result + n;
            }
        }
        return result;
    }
}