LeetCode [1512] Number of Good Pairs

 1512. Number of Good Pairs

Easy

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

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class Solution { public int numIdenticalPairs(int[] nums) { HashMap<Integer, Integer> counts = new HashMap<Integer, Integer>(); for(int v:nums) { if(counts.containsKey(v)) counts.put(v, counts.get(v)+1); else counts.put(v, 1); } int ret = 0; for(Map.Entry e : counts.entrySet()) { int n = (int) e.getValue(); if(n>1) { ret += n*(n-1)/2; } } return ret; } }