Link: https://leetcode.cn/problems/count-number-of-pairs-with-absolute-difference-k/

Question

difficulty: easy
adj diff: 1

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]
 

Constraints:

1 <= nums.length <= 200
1 <= nums[i] <= 100
1 <= k <= 99

这道题，我学会了 map.getOrDefault() 方法。

Code

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public int countKDifference(int[] nums, int k) {
    Map<Integer, Integer> map = new HashMap<Integer, Integer>();
    int count = 0;
    for (int i: nums) {
        // build map
        map.put(i, map.getOrDefault(i, 0) + 1);

        // count pairs
        count += map.getOrDefault(i + k, 0) + map.getOrDefault(i - k, 0);
    }
    return count;
}