Number of good pairs

Array Hash Table Math Counting

89.8% acceptance

Feb 25, 2026

5850

286

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.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn num_identical_pairs(nums: Vec<i32>) -> i32 {
    let mut count = std::collections::HashMap::new();
    let mut ans = 0;
    for x in nums {
      let c = count.entry(x).or_insert(0);
      ans += *c;
      *c += 1;
    }
    ans
  }
}