Longest String Chain — LeetCode 1048 Python Solution

The problem

You are given an array of words where each word consists of lowercase English letters. wordA is a predecessor of wordB if and only if we can insert exactly one letter anywhere in wordA without changing the order of the other characters to make it equal to wordB.

Example

Input

words = ["a","b","ba","bca","bda","bdca"]

Output

4

Explanation

One of the longest word chains is ["a","ba","bda","bdca"].

Python solution

class Solution:
    def longestStrChain(self, words: List[str]) -> int:
        def check(w1, w2):
            if len(w2) - len(w1) != 1:
                return False
            i = j = cnt = 0
            while i < len(w1) and j < len(w2):
                if w1[i] != w2[j]:
                    cnt += 1
                else:
                    i += 1
                j += 1
            return cnt < 2 and i == len(w1)

        n = len(words)
        dp = [1] * (n + 1)
        words.sort(key=lambda x: len(x))
        res = 1
        for i in range(1, n):
            for j in range(i):
                if check(words[j], words[i]):
                    dp[i] = max(dp[i], dp[j] + 1)
            res = max(res, dp[i])
        return res

Complexity

Pattern: Two Pointers

Use the order already in the input to discard half the search space at every step. LeetCode 1048. Longest String Chain is filed here because LeetCode tags it Two Pointers, which is the vocabulary this hub collects.

The two pointers guide has the Python template for the pattern and the 201 LeetCode problems that use it.

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