LeetCode 0820. Short Encoding of Words Solution in Java, C++, Python & Go | Explanation + Code

Description

A valid encoding of an array of words is any reference string s and array of indices indices such that:

• words.length == indices.length
• The reference string s ends with the '#' character.
• For each index indices[i], the substring of s starting from indices[i] and up to (but not including) the next '#' character is equal to words[i].

Given an array of words, return the length of the shortest reference string s possible of any valid encoding of words.

 

Example 1:

Input: words = ["time", "me", "bell"]
Output: 10
Explanation: A valid encoding would be s = "time#bell#" and indices = [0, 2, 5].
words[0] = "time", the substring of s starting from indices[0] = 0 to the next '#' is underlined in "time#bell#"
words[1] = "me", the substring of s starting from indices[1] = 2 to the next '#' is underlined in "time#bell#"
words[2] = "bell", the substring of s starting from indices[2] = 5 to the next '#' is underlined in "time#bell#"

Example 2:

Input: words = ["t"]
Output: 2
Explanation: A valid encoding would be s = "t#" and indices = [0].

 

Constraints:

• 1 <= words.length <= 2000
• 1 <= words[i].length <= 7
• words[i] consists of only lowercase letters.

Solutions

Solution 1

PythonJavaC++Go

class Trie: def __init__(self) -> None: self.children = [None] * 26 class Solution: def minimumLengthEncoding(self, words: List[str]) -> int: root = Trie() for w in words: cur = root for c in w[::-1]: idx = ord(c) - ord("a") if cur.children[idx] == None: cur.children[idx] = Trie() cur = cur.children[idx] return self.dfs(root, 1) def dfs(self, cur: Trie, l: int) -> int: isLeaf, ans = True, 0 for i in range(26): if cur.children[i] != None: isLeaf = False ans += self.dfs(cur.children[i], l + 1) if isLeaf: ans += l return ans(code-box)

class Trie { Trie[] children = new Trie[26]; } class Solution { public int minimumLengthEncoding(String[] words) { Trie root = new Trie(); for (String w : words) { Trie cur = root; for (int i = w.length() - 1; i >= 0; i--) { int idx = w.charAt(i) - 'a'; if (cur.children[idx] == null) { cur.children[idx] = new Trie(); } cur = cur.children[idx]; } } return dfs(root, 1); } private int dfs(Trie cur, int l) { boolean isLeaf = true; int ans = 0; for (int i = 0; i < 26; i++) { if (cur.children[i] != null) { isLeaf = false; ans += dfs(cur.children[i], l + 1); } } if (isLeaf) { ans += l; } return ans; } }(code-box)

struct Trie { Trie* children[26] = {nullptr}; }; class Solution { public: int minimumLengthEncoding(vector<string>& words) { auto root = new Trie(); for (auto& w : words) { auto cur = root; for (int i = w.size() - 1; i >= 0; --i) { if (cur->children[w[i] - 'a'] == nullptr) { cur->children[w[i] - 'a'] = new Trie(); } cur = cur->children[w[i] - 'a']; } } return dfs(root, 1); } private: int dfs(Trie* cur, int l) { bool isLeaf = true; int ans = 0; for (int i = 0; i < 26; ++i) { if (cur->children[i] != nullptr) { isLeaf = false; ans += dfs(cur->children[i], l + 1); } } if (isLeaf) { ans += l; } return ans; } };(code-box)

type trie struct { children [26]*trie } func minimumLengthEncoding(words []string) int { root := new(trie) for _, w := range words { cur := root for i := len(w) - 1; i >= 0; i-- { if cur.children[w[i]-'a'] == nil { cur.children[w[i]-'a'] = new(trie) } cur = cur.children[w[i]-'a'] } } return dfs(root, 1) } func dfs(cur *trie, l int) int { isLeaf, ans := true, 0 for i := 0; i < 26; i++ { if cur.children[i] != nil { isLeaf = false ans += dfs(cur.children[i], l+1) } } if isLeaf { ans += l } return ans }(code-box)

Solution 2

PythonJavaC++Go

class Trie: def __init__(self): self.children = [None] * 26 def insert(self, w): node = self pref = True for c in w: idx = ord(c) - ord("a") if node.children[idx] is None: node.children[idx] = Trie() pref = False node = node.children[idx] return 0 if pref else len(w) + 1 class Solution: def minimumLengthEncoding(self, words: List[str]) -> int: words.sort(key=lambda x: -len(x)) trie = Trie() return sum(trie.insert(w[::-1]) for w in words)(code-box)

class Trie { Trie[] children = new Trie[26]; int insert(String w) { Trie node = this; boolean pref = true; for (int i = w.length() - 1; i >= 0; --i) { int idx = w.charAt(i) - 'a'; if (node.children[idx] == null) { pref = false; node.children[idx] = new Trie(); } node = node.children[idx]; } return pref ? 0 : w.length() + 1; } } class Solution { public int minimumLengthEncoding(String[] words) { Arrays.sort(words, (a, b) -> b.length() - a.length()); int ans = 0; Trie trie = new Trie(); for (String w : words) { ans += trie.insert(w); } return ans; } }(code-box)

class Trie { public: vector<Trie*> children; Trie() : children(26) {} int insert(string w) { Trie* node = this; bool pref = true; for (char c : w) { c -= 'a'; if (!node->children[c]) { pref = false; node->children[c] = new Trie(); } node = node->children[c]; } return pref ? 0 : w.size() + 1; } }; class Solution { public: int minimumLengthEncoding(vector<string>& words) { sort(words.begin(), words.end(), [](string& a, string& b) { return a.size() > b.size(); }); Trie* trie = new Trie(); int ans = 0; for (auto& w : words) { reverse(w.begin(), w.end()); ans += trie->insert(w); } return ans; } };(code-box)

type Trie struct { children [26]*Trie } func newTrie() *Trie { return &Trie{} } func (this *Trie) insert(w string) int { node := this pref := true for i := len(w) - 1; i >= 0; i-- { idx := w[i] - 'a' if node.children[idx] == nil { pref = false node.children[idx] = newTrie() } node = node.children[idx] } if pref { return 0 } return len(w) + 1 } func minimumLengthEncoding(words []string) int { sort.Slice(words, func(i, j int) bool { return len(words[i]) > len(words[j]) }) trie := newTrie() ans := 0 for _, w := range words { ans += trie.insert(w) } return ans }(code-box)