How should I practice Count String Pairs With Disjoint Characters?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Netflix phone screen problems in FastPrep.

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FastPrep tags this as a Netflix phone screen coding practice problem when the problem catalog has that company and stage context.

Count String Pairs With Disjoint Characters

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Problem statement

Given an array of strings words, return the number of unordered index pairs (i, j) such that i < j and the two strings share no character.

For this exercise, assume every array index is a distinct candidate, even when two strings have equal values. Every string contains only lowercase English letters and may be empty. An empty string shares no character with any string.

Function

countDisjointCharacterPairs(words: String[]) → int

Examples

Example 1

words = ["abc","def","ad","xyz"]return = 4

The valid pairs are (0,1), (0,3), (1,3), and (2,3).

Example 2

words = ["a","a","b",""]return = 5

The two equal a values occupy different indices. Each pairs with b and the empty string, while b also pairs with the empty string.

Example 3

words = []return = 0

An empty array contains no index pair.

Constraints

0 <= words.length <= 5000
0 <= sum(words[i].length) <= 200000
Every string contains only lowercase English letters and may be empty.
Each array index is counted as a distinct candidate.