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2006 Count Number of Pairs With Absolute Difference K

Given an integer array nums and an integer k, return the number of pairs (i, j) where i < j such that |nums[i] - nums[j]| == k.

The value of |x| is defined as:

  • x if x >= 0.
  • -x if x < 0.

Example 1:

Input: nums = [1,2,2,1], k = 1
Output: 4
Explanation: The pairs with an absolute difference of 1 are:
- [1,2,2,1]
- [1,2,2,1]
- [1,2,2,1]
- [1,2,2,1]

Example 2:

Input: nums = [1,3], k = 3
Output: 0
Explanation: There are no pairs with an absolute difference of 3.

Example 3:

Input: nums = [3,2,1,5,4], k = 2
Output: 3
Explanation: The pairs with an absolute difference of 2 are:
- [3,2,1,5,4]
- [3,2,1,5,4]
- [3,2,1,5,4]

Solution:

class Solution {
    public int countKDifference(int[] nums, int k) {
        Map<Integer, Integer> map = new HashMap<>();
        int result = 0;

        for (int i = 0; i < nums.length; i++){
            if (map.containsKey(nums[i] - k) ){
                result = result + map.get(nums[i]-k);
            }

            if (map.containsKey(nums[i] + k)){
                result = result + map.get(nums[i]+k);
            }

            map.put(nums[i], map.getOrDefault(nums[i],0)+1);
        }

        return result;
    }
}

// TC: O(n)
// SC: O(n)