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Grokking the Coding Interview Patterns in C++

Solution: Count Pairs in Two Arrays

Explore how to efficiently count index pairs in two arrays where the sum from one array is greater than the other by using sorting and binary search. This lesson helps you understand the reduction of a problem using difference arrays and the optimization from a brute force O(n²) method to O(n log n), improving your problem-solving skills in coding interviews.

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Statement

You are given two positive integer arrays, nums1 and nums2, both of length nn. Your task is to count and return the number of pairs of indexes (i,j)(i, j) where:

  • i<ji < j , and

  • nums1[i]+nums1[j]>nums2[i]+nums2[j]\text{nums1}[i] + \text{nums1}[j] > \text{nums2}[i] + \text{nums2}[j]

In simpler terms, the sum of two elements from nums1 must be greater than that of the corresponding elements from nums2.

Constraints:

  • n=n = ...