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.



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].

Difficulty: introductory

Starter code:

class Solution:
    def findPairs(self, nums: List[int], k: int) -> int:
        

Solutions:
class Solution:
     def findPairs(self, nums, k):
         """
         :type nums: List[int]
         :type k: int
         :rtype: int
         """
         # import collections
         # unique_nums = set(nums)
         # count = 0
         # new_nums = collections.Counter(nums)
         # if k == 0:
         #     for i in unique_nums:
         #         if new_nums[i] > 1:
         #             count +=1
         #     return count
         # elif k < 0:
         #     return 0
         # elif k > 0:
         #     for i in unique_nums:
         #         if i+k in unique_nums:
         #             count += 1
         #     return count
         
 # 用counter来做
         # import collections
         # count = 0
         # list_nums = set(nums)
         # if k == 0:
         #     nums = collections.Counter(nums)
         #     for each in nums:
         #         if nums[each] > 1:
         #             count += 1
         #     return count
         # elif k < 0:
         #     return 0
         # elif k > 0:
         #     for i in list_nums:
         #         if i + k in list_nums:
         #             count += 1
         #     return count
         
 # 用dict来做
 
         count = 0
         if k < 0 :
             return count
         if k == 0:
             new_nums = collections.defaultdict(int)
             for i in nums:
                 new_nums[i] +=1
             for value in new_nums:
                 if new_nums[value] > 1:
                     count += 1
             return count
         if k > 0 :
             nums = set(nums)
             for i in nums:
                 if i+k in nums:
                     count += 1
             return count
 
 #         if k < 0:
 #             return 0
 #         if k == 0:
 #             dict = collections.defaultdict(int)
 #             for i in nums:
 #                 dict[i] += 1
 #             ans = 0
 #             for value in dict.values():
 #                 if value > 1:
 #                     ans += 1
 #             return ans
 #         nums = set(nums)
 #         ans = 0
 #         for item in nums:
 #             if item+k in nums:
 #                 ans += 1
 #         return ans


class Solution:
     def findPairs(self, nums, k):
         """
         :type nums: List[int]
         :type k: int
         :rtype: int
         """
         # import collections
         # unique_nums = set(nums)
         # count = 0
         # new_nums = collections.Counter(nums)
         # if k == 0:
         #     for i in unique_nums:
         #         if new_nums[i] > 1:
         #             count +=1
         #     return count
         # elif k < 0:
         #     return 0
         # elif k > 0:
         #     for i in unique_nums:
         #         if i+k in unique_nums:
         #             count += 1
         #     return count
         
 # 用counter来做
         # import collections
         # count = 0
         # list_nums = set(nums)
         # if k == 0:
         #     nums = collections.Counter(nums)
         #     for each in nums:
         #         if nums[each] > 1:
         #             count += 1
         #     return count
         # elif k < 0:
         #     return 0
         # elif k > 0:
         #     for i in list_nums:
         #         if i + k in list_nums:
         #             count += 1
         #     return count
         
 # 用dict来做
 
         count = 0
         if k < 0 :
             return count
         if k == 0:
             new_nums = collections.defaultdict(int)
             for i in nums:
                 new_nums[i] +=1
             for j in new_nums:
                 if new_nums[j] > 1:
                     count += 1
             return count
         if k > 0 :
             nums = set(nums)
             for i in nums:
                 if i+k in nums:
                     count += 1
             return count
 
 #         if k < 0:
 #             return 0
 #         if k == 0:
 #             dict = collections.defaultdict(int)
 #             for i in nums:
 #                 dict[i] += 1
 #             ans = 0
 #             for value in dict.values():
 #                 if value > 1:
 #                     ans += 1
 #             return ans
 #         nums = set(nums)
 #         ans = 0
 #         for item in nums:
 #             if item+k in nums:
 #                 ans += 1
 #         return ans


class Solution:
     def findPairs(self, nums, k):
         """
         :type nums: List[int]
         :type k: int
         :rtype: int
         """
         import collections
         count = 0
         list_nums = set(nums)
         if k == 0:
             nums = collections.Counter(nums)
             for each in nums:
                 if nums[each] > 1:
                     count += 1
             return count
         elif k < 0:
             return 0
         elif k > 0:
             for i in list_nums:
                 if i + k in list_nums:
                     count += 1
             return count


class Solution:
     def findPairs(self, nums, k):
         """
         :type nums: List[int]
         :type k: int
         :rtype: int
         """
         dic = {}
         count = 0
         if(k<0):
             return 0
         if(len(nums) == 1 or len(nums) == 0):
             return 0
         dic[nums[0]] = 1
         if(k == 0):
             for i in range(1,len(nums)):
                 if(nums[i] in dic and dic[nums[i]]==1):
                     dic[nums[i]] += 1
                     count += 1
                 elif(nums[i] not in dic):
                     dic[nums[i]] = 1
                 else:
                     dic[nums[i]] += 1
                 
         else:
             for i in range(1,len(nums)):
                 if((nums[i]-k) in dic and nums[i] not in dic):
                     count += 1
                 if((nums[i]+k) in dic and nums[i] not in dic):
                     count += 1
                 dic[nums[i]] = 1
 
                 
         return count

class Solution:
     def findPairs(self, nums, k):
         """
         :type nums: List[int]
         :type k: int
         :rtype: int
         """
         if k < 0:
             return 0
         result, lookup = set(), set()
         for num in nums:
             if num+k in lookup:
                 result.add(num)
             if num-k in lookup:
                 result.add(num-k)
             lookup.add(num)
         return len(result)
                        


class Solution:
     def findPairs(self, nums, k):
         """
         :type nums: List[int]
         :type k: int
         :rtype: int
         """
         if k < 0:
             return 0
         
         from collections import Counter
         c = Counter(nums)
             
         if k == 0:
             return sum([1 for num, count in list(c.items()) if count > 1])
         else:
             return sum([1 for num, _ in list(c.items()) if num + k in c])


class Solution:
     def findPairs(self, nums, k):
         """
         :type nums: List[int]
         :type k: int
         :rtype: int
         """
         
         if k < 0:
             return 0
         
         unique = {}
         for num in nums:
             unique[num] = unique.get(num, 0) + 1
         
         res = 0
         for num in unique:
             if k == 0:
                 if unique[num] > 1:
                     res += 1
             else:
                 if num+k in unique :
                     res += 1
                 
         return res 

class Solution:
     def findPairs(self, nums, k):
         """
         :type nums: List[int]
         :type k: int
         :rtype: int
         """
         
         ### 2 pointers
         # result = 0;
         # nums.sort()
         # for i in range(len(nums) - 1):
         #     if i == 0 or (i != 0 and nums[i] != nums[i - 1]):
         #         for j in range(i + 1, len(nums)):
         #             if nums[j] - nums[i] == k:
         #                 result += 1
         #                 break
         #             elif nums[j] - nums[i] > k:
         #                 break
         # return result
         
         ### map
         result = 0
         c = collections.Counter(nums)
         for i in c:
             if k > 0 and i + k in c or k == 0 and c[i] > 1:
                 result += 1
         return result


class Solution:
     def findPairs(self, nums, k):
         """ Returns number of unique k-diff pairs(i, j) such as |i - j| = k.
         Algorithm based on hashing.
 
         Time complexity: O(n). Space complexity: O(n), n is len(nums).
         """
         num_count = dict()
         for n in nums:
             num_count[n] = num_count.get(n, 0) + 1
 
         total = 0
         for n in num_count:
             if k == 0 and num_count[n] > 1:
                 total += 1
             elif k > 0 and (n + k) in num_count:
                 total += 1
         return total
 


class Solution:
     def findPairs(self, nums, k):
         """
         :type nums: List[int]
         :type k: int
         :rtype: int
         """
         s = set(nums)
         total = 0
         if k < 0:
             return 0
         if k:
             for x in s:
                 if x + k in s:
                     total += 1
         else:
             counter = collections.Counter(nums)
             for k, v in counter.items():
                 if v > 1:
                     total += 1
         return total

class Solution:
     def findPairs(self, nums, k):
         """
         :type nums: List[int]
         :type k: int
         :rtype: int
         """
         
         if len(nums) < 2 or k < 0:
             return 0
         
         count = 0
         nums.sort()
         i, j = 0, 1
         while i < len(nums) - 1 and j < len(nums):
             j = max(i+1, j)
             d = nums[j] - nums[i]
             if d < k:
                 j += 1
             elif d == k:
                 count += 1
                 while (i + 1) < len(nums) and nums[i] == nums[i + 1]:
                     i += 1
                 i += 1
             else:
                 i += 1
 
         
         return count


class Solution:
     def findPairs(self, nums, k):
         """
         :type nums: List[int]
         :type k: int
         :rtype: int
         """
         if k<0:
             return 0
         
         pairs={}
         
         cnt = 0
         
         for a in nums:            
             if not a in pairs:
                 if a+k in pairs and a not in pairs[a+k]:
                     pairs[a+k].append(a)
                     cnt +=1
                 if a-k in pairs and a not in pairs[a-k]:
                     pairs[a-k].append(a)
                     cnt +=1
                 pairs[a]=[]
             else:
                 if not a+k in pairs[a]:
                     if a+k in pairs and a not in pairs[a+k]:
                         pairs[a+k].append(a)
                         cnt +=1
                 if not a-k in pairs[a]:
                     if a-k in pairs and a not in pairs[a-k]:
                         pairs[a-k].append(a)
                         cnt+=1
             
         return cnt