1048. Longest String Chain

Description

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.

  • For example, "abc" is a predecessor of "abac", while "cba" is not a predecessor of "bcad".

A word chain is a sequence of words [word1, word2, ..., wordk] with k >= 1, where word1 is a predecessor of word2, word2 is a predecessor of word3, and so on. A single word is trivially a word chain with k == 1.

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

 

Example 1:

Input: words = ["a","b","ba","bca","bda","bdca"]
Output: 4
Explanation: One of the longest word chains is ["a","ba","bda","bdca"].

Example 2:

Input: words = ["xbc","pcxbcf","xb","cxbc","pcxbc"]
Output: 5
Explanation: All the words can be put in a word chain ["xb", "xbc", "cxbc", "pcxbc", "pcxbcf"].

Example 3:

Input: words = ["abcd","dbqca"]
Output: 1
Explanation: The trivial word chain ["abcd"] is one of the longest word chains.
["abcd","dbqca"] is not a valid word chain because the ordering of the letters is changed.

 

Constraints:

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

Solutions

Solution 1

Python Code
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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

Java Code
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class Solution {
    public int longestStrChain(String[] words) {
        Arrays.sort(words, Comparator.comparingInt(String::length));
        int res = 0;
        Map<String, Integer> map = new HashMap<>();
        for (String word : words) {
            int x = 1;
            for (int i = 0; i < word.length(); ++i) {
                String pre = word.substring(0, i) + word.substring(i + 1);
                x = Math.max(x, map.getOrDefault(pre, 0) + 1);
            }
            map.put(word, x);
            res = Math.max(res, x);
        }
        return res;
    }
}

C++ Code
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class Solution {
public:
    int longestStrChain(vector<string>& words) {
        sort(words.begin(), words.end(), [&](string a, string b) { return a.size() < b.size(); });
        int res = 0;
        unordered_map<string, int> map;
        for (auto word : words) {
            int x = 1;
            for (int i = 0; i < word.size(); ++i) {
                string pre = word.substr(0, i) + word.substr(i + 1);
                x = max(x, map[pre] + 1);
            }
            map[word] = x;
            res = max(res, x);
        }
        return res;
    }
};

Go Code
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func longestStrChain(words []string) int {
	sort.Slice(words, func(i, j int) bool { return len(words[i]) < len(words[j]) })
	res := 0
	mp := make(map[string]int)
	for _, word := range words {
		x := 1
		for i := 0; i < len(word); i++ {
			pre := word[0:i] + word[i+1:len(word)]
			x = max(x, mp[pre]+1)
		}
		mp[word] = x
		res = max(res, x)
	}
	return res
}

TypeScript Code
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function longestStrChain(words: string[]): number {
    words.sort((a, b) => a.length - b.length);
    let ans = 0;
    let hashTable = new Map();
    for (let word of words) {
        let c = 1;
        for (let i = 0; i < word.length; i++) {
            let pre = word.substring(0, i) + word.substring(i + 1);
            c = Math.max(c, (hashTable.get(pre) || 0) + 1);
        }
        hashTable.set(word, c);
        ans = Math.max(ans, c);
    }
    return ans;
}

Rust Code
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use std::collections::HashMap;

impl Solution {
    #[allow(dead_code)]
    pub fn longest_str_chain(words: Vec<String>) -> i32 {
        let mut words = words;
        let mut ret = 0;
        let mut map: HashMap<String, i32> = HashMap::new();

        // Sort the words vector first
        words.sort_by(|lhs, rhs| { lhs.len().cmp(&rhs.len()) });

        // Begin the "dp" process
        for w in words.iter() {
            let n = w.len();
            let mut x = 1;

            for i in 0..n {
                let s = w[..i].to_string() + &w[i + 1..];
                let v = map.entry(s.clone()).or_default();
                x = std::cmp::max(x, *v + 1);
            }

            map.insert(w.clone(), x);

            ret = std::cmp::max(ret, x);
        }

        ret
    }
}

Solution 2

Python Code
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class Solution:
    def longestStrChain(self, words: List[str]) -> int:
        words.sort(key=lambda x: len(x))
        res = 0
        mp = {}
        for word in words:
            x = 1
            for i in range(len(word)):
                pre = word[:i] + word[i + 1 :]
                x = max(x, mp.get(pre, 0) + 1)
            mp[word] = x
            res = max(res, x)
        return res