Bookend Word Pairs

Easy

Say that a word a bookends a word b if b both starts and ends with a. For example, "aba" bookends "ababa", while "ab" does not bookend "abc". Every word bookends itself. Given the list words, return the number of index pairs i < j where words[i] bookends words[j].

Example 1

words=["ok", "okok", "o", "oko"] → 2

The pairs are "ok" with "okok" and "o" with "oko". "okok" is not framed by "o" because it ends in k.

Example 2

words=["abcab", "ab"] → 0

The short word comes after the long one, and only pairs where the framing word comes first count.

Example 3

words=["x", "x", "xx"] → 3

All three pairs count: "x"–"x", "x"–"xx", and the second "x"–"xx".

Constraints

1 ≤ len(words) ≤ 50
1 ≤ len(words[i]) ≤ 20
Words consist of lowercase English letters

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Trie Array String String Matching Hash Function Rolling Hash

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Input

words=["ok", "okok", "o", "oko"]

Expected

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