k-diff-pairs-in-an-array.js

/**
 * K-diff Pairs in an Array
 *
 * Given an array of integers and an integer k, you need to find the number of unique k-diff pairs in the array.
 * Here a k-diff pair is defined as an integer pair (i, j), where i and j are both numbers in the array and their
 * absolute difference is k.
 *
 * Example 1:
 *
 * Input: [3, 1, 4, 1, 5], k = 2
 * Output: 2
 *
 * Explanation: There are two 2-diff pairs in the array, (1, 3) and (3, 5).
 * Although we have two 1s in the input, we should only return the number of unique pairs.
 *
 * Example 2:
 *
 * Input:[1, 2, 3, 4, 5], k = 1
 * Output: 4
 *
 * Explanation: There are four 1-diff pairs in the array, (1, 2), (2, 3), (3, 4) and (4, 5).
 *
 * Example 3:
 *
 * Input: [1, 3, 1, 5, 4], k = 0
 * Output: 1
 *
 * Explanation: There is one 0-diff pair in the array, (1, 1).
 */

/**
 * @param {number[]} nums
 * @param {number} k
 * @return {number}
 */
const findPairs = (nums, k) => {
  // Step 1. Count the characters
  const map = {};
  for (let num of nums) {
    map[num] = ~~map[num] + 1;
  }

  // Step 2. Count the pairs
  let count = 0;
  for (let key in map) {
    if (k === 0 && map[key] > 1) {
      count++;
    } else if (k > 0 && parseInt(key) + k in map) {
      count++;
    }
  }

  return count;
};

export { findPairs };