Longest String Chain Python Solution

 Given a list of words, each word consists of English lowercase letters.

Let's say word1 is a predecessor of word2 if and only if we can add exactly one letter anywhere in word1 to make it equal to word2.  For example, "abc" is a predecessor of "abac".

A word chain is a sequence of words [word_1, word_2, ..., word_k] with k >= 1, where word_1 is a predecessor of word_2, word_2 is a predecessor of word_3, and so on.

Return the longest possible length of a word chain with words chosen from the given list of words.

 

Example 1:

Input: ["a","b","ba","bca","bda","bdca"]
Output: 4
Explanation: one of the longest word chain is "a","ba","bda","bdca".

class Solution:
    def longestStrChain(self, words: List[str]) -> int:
        if not words:
            return 1
        words.sort(key=len)
        cache = {}
        res = 0
        for word in words:
            longest = 0
            for i in range(len(word)):
                child = word[0:i]+word[i+1:]
                longest = max(longest,cache.get(child,0)+1)
            cache[word] = longest
            res = max(res,longest)
        return res

TC:O(N log n) or O(N * max(len(word))) SC: O(N)