KdiffPairsInanArray.java

/* (C) 2024 YourCompanyName */
package hashing;

import java.util.HashMap;
import java.util.Map;

/**
 * Created by gouthamvidyapradhan on 28/03/2017. 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.
 *
 * <p>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). Note: The pairs
 * (i, j) and (j, i) count as the same pair. The length of the array won't exceed 10,000. All the
 * integers in the given input belong to the range: [-1e7, 1e7].
 */
public class KdiffPairsInanArray {
  private Map<Integer, Integer> map = new HashMap<>();
  private int count = 0;

  /**
   * Main method
   *
   * @param args
   * @throws Exception
   */
  public static void main(String[] args) throws Exception {
    int[] nums = {1, 2, 3, 4, 5};
    System.out.println(new KdiffPairsInanArray().findPairs(nums, -1));
  }

  public int findPairs(int[] nums, int k) {
    if (nums.length == 0 || k < 0) return 0;
    for (int i : nums) {
      map.put(i, map.getOrDefault(i, 0) + 1);
    }
    for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
      if (k == 0) {
        if (entry.getValue() > 1) count++;
      } else {
        if (map.containsKey(entry.getKey() + k)) count++;
      }
    }
    return count;
  }
}