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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

• Java
• C++
• Python
• Go
• TypeScript
• RenderScript

• 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;
      }
  }
  

• 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;
      }
  };
  

• 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
  
  

• 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
  }
  

• 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;
  }
  
  

• 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
      }
  }
  
  

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