1512. Number of Good Pairs

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題目敘述

Given an array of integers nums, return the number of good pairs.

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

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

解題思路

Solution

import java.util.HashMap;
import java.util.Map;

class Solution {
    public int numIdenticalPairs(int[] nums) {
        Map<Integer, Integer> map = new HashMap<>();
        
        for(int num : nums){
            map.put(num, map.getOrDefault(num, 0) + 1);
        }

        int ans = 0;
        for(int key : map.keySet()){
            for(int i = map.get(key) - 1; i > 0; i--){
                ans += i;
            }
        }

        return ans;
    }
}