1512 - Number of Good Pairs

1512. Number of Good Pairs

Problem Statement

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

Click to open Hints

• Count how many times each number appears. If a number appears n times, then n * (n – 1) // 2 good pairs can be made with this number.

Solutions

Rust

impl Solution {
    pub fn num_identical_pairs(nums: Vec<i32>) -> i32 {
        let mut count = 0;
        let mut map = std::collections::HashMap::new();

        for num in nums {
            let entry = map.entry(num).or_insert(0);
            count += *entry;
            *entry += 1;
        }

        count
    }
}

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