1048 Longest String Chain

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".

Note:

1 <= words.length <= 1000
1 <= words[i].length <= 16
words[i] only consists of English lowercase letters.

Clean Code

class Solution {
public:
    static bool compare(const string &s1, const string &s2) {
        return s1.length() < s2.length();
    }

    int longestStrChain(vector<string>& words) {
        sort(words.begin(), words.end(), compare);
        unordered_map<string, int> dp;
        int res = 0;
        for (string w : words) {
            int best = 0;
            for (int i = 0; i < w.length(); i++) {
                string word = w.substr(0, i) + w.substr(i + 1);
                best = max(best, dp[word] + 1);
            }
            dp[w] = best;
            res = max(res, best);
        }
        return res;
    }
}