KDifferencePairs.java

package Leetcode;

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

/**
 * Given an array of integers nums and an integer k, return the number of unique k-diff pairs in the array.
 *
 * A k-diff pair is an integer pair (nums[i], nums[j]), where the following are true:
 *
 * 0 <= i, j < nums.length
 * i != j
 * |nums[i] - nums[j]| == k
 * Notice that |val| denotes the absolute value of val.
 *
 *
 *
 * Example 1:
 *
 * Input: nums = [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: nums = [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: nums = [1,3,1,5,4], k = 0
 * Output: 1
 * Explanation: There is one 0-diff pair in the array, (1, 1).
 * Example 4:
 *
 * Input: nums = [1,2,4,4,3,3,0,9,2,3], k = 3
 * Output: 2
 * Example 5:
 *
 * Input: nums = [-1,-2,-3], k = 1
 * Output: 2
 *
 *
 * Constraints:
 *
 * 1 <= nums.length <= 104
 * -107 <= nums[i] <= 107
 * 0 <= k <= 107
 */

public class KDifferencePairs {
    public static int findPairs(int[] nums, int k) {
        if(nums == null || nums.length == 0 || k < 0)
            return 0;

        Map<Integer, Integer> map = new HashMap<>();
        int result = 0;

        for(int i : nums) {
            map.put(i, map.getOrDefault(i, 0) + 1);
        }

        for(int key : map.keySet()) {
            if (k == 0) {
                // Need to check if there are two same numbers that satisfies this condition.
                if(map.get(key) >= 2)
                    result++;
            } else {
                if(map.containsKey(key + k)) // Only count (key + k) to avoud duplicate
                    result++;
            }
        }
        return result;
    }

    public static void main(String[] args) {
        int[] nums = new int[]{3,1,4,1,5};
        int[] nums2 = new int[]{1,3,1,5,4};
        System.out.println(findPairs(nums, 2));
        System.out.println(findPairs(nums2, 0));
    }
}