LeetCode 1512. Number of Good Pairs

Description

https://leetcode.com/problems/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

Explanation

Created a dictionary with same number item as groups.

Python Solution

class Solution:
    def numIdenticalPairs(self, nums: List[int]) -> int:
        count = 0
        visited = defaultdict(list)
        
        for i, num in enumerate(nums):
            if num in visited:
                count += len(visited[num])
            visited[num].append(i)
                
        return count
            
  • Time Complexity: O(N)
  • Space Complexity: O(N)

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