03. K-diff Pairs in an Array.cpp

/*
K-diff Pairs in an Array
========================

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
*/

/* Language: C++ 
==================
*/

class Solution
{
public:
  int findPairs(vector<int> &nums, int k)
  {
    unordered_map<int, int> m;
    for (auto i : nums)
      m[i]++;
    int ans = 0;
    for (auto it : m)
    {
      int num = it.first;
      if (k == 0 && it.second > 1)
        ans++;
      else if (k != 0 && m.find(k + it.first) != m.end())
        ans++;
    }
    return ans;
  }
};