# 1865. Finding Pairs With a Certain Sum from collections import Counter """ you are given two integer arrays 'nums1' and 'nums2'. you are tasked to implement a data structure that supports queries of two types: add a positive integer to an element of a given index in the array 'nums2', count the number of pairs '(i, j)' such that 'nums1[i] + nums2[i]' equals a given ('0 <= i < nums1.length' and '0 <= j < nums2.length') implement the 'FindSumPairs' class. """ class FindSumPairs(object): def __init__(self, nums1, nums2): """ :type nums1: List[int] :type nums2: List[int] """ self.nums1_dict = Counter(nums1) self.nums2_dict = Counter(nums2) self.nums2 = nums2 def add(self, index, val): """ :type index: int :type val: int :rtype: None """ prev = self.nums2[index] self.nums2[index] += val self.nums2_dict[prev] -= 1 self.nums2_dict[prev + val] += 1 def count(self, tot): """ :type tot: int :rtype: int """ ans = 0 for i, j in self.nums1_dict.items(): ans += j * self.nums2_dict[tot - i] return ans if __name__ == "__main__": obj = FindSumPairs(nums1=[1, 1, 2, 2, 2, 3], nums2=[1, 4, 5, 2, 5, 4]) print(obj.count(7)) print(obj.add(3, 2)) print(obj.count(8)) print(obj.count(4)) print(obj.add(0, 1)) print(obj.add(1, 1)) print(obj.count(7))