Formatted question description: https://leetcode.ca/all/1048.html
1048. Longest String Chain (Medium)
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.
Related Topics:
Hash Table, Dynamic Programming
Solution 1.
// OJ: https://leetcode.com/problems/longest-string-chain/
// Time: O(N^2)
// Space: O(N)
class Solution {
public:
int longestStrChain(vector<string>& A) {
int N = A.size(), ans = 1;
vector<int> id(N), len(N, 1);
iota(begin(id), end(id), 0);
sort(begin(id), end(id), [&](int a, int b) { return A[a].size() < A[b].size(); });
vector<array<int, 26>> cnts(N);
map<int, vector<int>> m;
for (int i = 0; i < N; ++i) {
for (char c : A[i]) cnts[i][c - 'a']++;
m[A[i].size()].push_back(i);
}
for (auto &[cnt, ids] : m) {
if (m.count(cnt - 1) == 0) continue;
for (int i : ids) {
for (int j : m[cnt - 1]) {
int diff = 0;
for (int k = 0; k < 26; ++k) {
diff += abs(cnts[i][k] - cnts[j][k]);
if (diff > 1) break;
}
if (diff == 1) len[i] = max(len[i], len[j] + 1);
}
ans = max(ans, len[i]);
}
}
return ans;
}
};
Solution 2.
// OJ: https://leetcode.com/problems/longest-string-chain/
// Time: O(NSS)
// Space: O(NS)
// Ref: https://leetcode.com/problems/longest-string-chain/discuss/294890/C%2B%2BJavaPython-DP-Solution
class Solution {
public:
int longestStrChain(vector<string>& A) {
auto cmp = [](string &a, string &b) { return a.size() < b.size(); };
sort(begin(A), end(A), cmp);
unordered_map<string, int> dp;
int ans = 1;
for (auto &s : A) {
for (int i = 0; i < s.size(); ++i) {
dp[s] = max(dp[s], dp[s.substr(0, i) + s.substr(i + 1)] + 1);
ans = max(ans, dp[s]);
}
}
return ans;
}
};
Java
-
class Solution { public int longestStrChain(String[] words) { Arrays.sort(words, new Comparator<String>() { public int compare(String str1, String str2) { if (str1.length() != str2.length()) return str1.length() - str2.length(); else return str1.compareTo(str2); } }); int smallestLength = words[0].length(); int nextLength = smallestLength + 1; int length = words.length; int[] dp = new int[length]; int dpStartIndex = -1; for (int i = 0; i < length; i++) { dp[i] = 1; if (words[i].length() == nextLength && dpStartIndex < 0) dpStartIndex = i; } if (dpStartIndex < 0) return 1; for (int i = dpStartIndex; i < length; i++) { String curWord = words[i]; for (int j = i - 1; j >= 0; j--) { String prevWord = words[j]; if (prevWord.length() == curWord.length()) continue; else if (prevWord.length() < curWord.length() - 1) break; else { if (isSubsequence(prevWord, curWord)) dp[i] = Math.max(dp[i], dp[j] + 1); } } } int maxLength = 0; for (int num : dp) maxLength = Math.max(maxLength, num); return maxLength; } public boolean isSubsequence(String str1, String str2) { int length1 = str1.length(), length2 = str2.length(); if (length1 > length2) return false; int index1 = 0, index2 = 0; while (index1 < length1 && index2 < length2) { char c1 = str1.charAt(index1), c2 = str2.charAt(index2); if (c1 == c2) index1++; index2++; } return index1 == length1; } }
-
// OJ: https://leetcode.com/problems/longest-string-chain/ // Time: O(N * S^2) // Space: O(NS) class Solution { unordered_map<string, int> m; int dp(const string &s) { if (m[s]) return m[s]; if (s.size() == 1) return 1; int ans = 1; for (int i = 0; i < s.size(); ++i) { auto copy = s; copy.erase(begin(copy) + i); if (m.count(copy)) { ans = max(ans, 1 + dp(copy)); } } return m[s] = ans; } public: int longestStrChain(vector<string>& A) { for (auto &s : A) m[s] = 0; int ans = 0; for (const auto &[s, len] : m) { ans = max(ans, dp(s)); } return ans; } };
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# 1048. Longest String Chain # https://leetcode.com/problems/longest-string-chain/ class Solution: def longestStrChain(self, words: List[str]) -> int: dp = {} res = 1 for word in sorted(words, key = len): dp[word] = 1 for i in range(len(word)): prev = word[:i] + word[i + 1:] if prev in dp: dp[word] = max(dp[word], dp[prev] + 1) res = max(res, dp[word]) return res