# 1512. Number of Good Pairs

## Description

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

Constraints:

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

## Solutions

• class Solution {
public int numIdenticalPairs(int[] nums) {
int ans = 0;
int[] cnt = new int[101];
for (int x : nums) {
ans += cnt[x]++;
}
return ans;
}
}

• class Solution {
public:
int numIdenticalPairs(vector<int>& nums) {
int ans = 0;
int cnt[101]{};
for (int& x : nums) {
ans += cnt[x]++;
}
return ans;
}
};

• class Solution:
def numIdenticalPairs(self, nums: List[int]) -> int:
ans = 0
cnt = Counter()
for x in nums:
ans += cnt[x]
cnt[x] += 1
return ans

• func numIdenticalPairs(nums []int) (ans int) {
cnt := [101]int{}
for _, x := range nums {
ans += cnt[x]
cnt[x]++
}
return
}

• function numIdenticalPairs(nums: number[]): number {
const cnt = new Array(101).fill(0);
let ans = 0;
for (const x of nums) {
ans += cnt[x]++;
}
return ans;
}

• class Solution {
/**
* @param Integer[] $nums * @return Integer */ function numIdenticalPairs($nums) {
$arr = array_values(array_unique($nums));
for ($i = 0;$i < count($nums);$i++) {
$v[$nums[$i]] += 1; }$rs = 0;
for ($j = 0;$j < count($arr);$j++) {
$rs += ($v[$arr[$j]] * ($v[$arr[$j]] - 1)) / 2; } return$rs;
}
}

• impl Solution {
pub fn num_identical_pairs(nums: Vec<i32>) -> i32 {
let mut cnt = [0; 101];
let mut ans = 0;
for &num in nums.iter() {
ans += cnt[num as usize];
cnt[num as usize] += 1;
}
ans
}
}