K_Diff_Unique_Pairs.py

def findPairs(self, nums, k):
    if k < 0 or not nums: return 0
    lookingFor = {}; pairs = 0
    for i in range(len(nums)):
        lookingFor[nums[i]] = lookingFor.get(nums[i], 0) + 1
    for i in lookingFor:
        if k == 0:
            if lookingFor[i] > 1: 
                pairs += 1
        else:
            if k + i in lookingFor: 
                pairs += 1
    return pairs