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Author: assassint2017

Longest Word in Dictionary/Longest_Word_in_Dictionary.cpp

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+// 首先需要对给定的字典建立一个前缀树，然后使用深度优先搜索进行查找
+
+// Runtime: 52 ms, faster than 84.90% of C++ online submissions for Longest Word in Dictionary.
+// Memory Usage: 29.5 MB, less than 30.00% of C++ online submissions for Longest Word in Dictionary.
+
+struct TrieNode
+{
+    bool isWord = false;
+    TrieNode* next[26] = {nullptr};
+};
+
+class Solution 
+{
+public:
+
+    Solution () : root(new TrieNode()) {}
+
+    ~Solution () { clear(root); }
+
+    string longestWord(vector<string>& words) 
+    {
+        // 建立字典树
+        buildTire(words);
+        
+        string res = "", candidate = "";
+
+        dfs(root, res, candidate);
+        
+        return res;
+    }
+private:
+    TrieNode* root = nullptr;
+    
+private:
+    void buildTire(vector<string>& words)
+    {   
+        // 迭代插入
+        for (auto word : words)
+        {
+            TrieNode* head = root;
+            
+            for (int index = 0; index < word.length(); ++index)
+            {
+                if (head->next[word[index] - 'a'] == nullptr)
+                {
+                    TrieNode* node = new TrieNode();
+                    head->next[word[index] - 'a'] = node;
+                }
+                head = head->next[word[index] - 'a'];
+                if (index == word.length() - 1)
+                    head->isWord = true;
+            }
+        }
+    }
+    
+    void dfs(TrieNode* root, string& res, string& candidate)
+    {
+        if (root == nullptr)
+            return ;
+        
+        for (int i = 0; i < 26; ++i)
+        {
+            if (root->next[i] != nullptr && root->next[i]->isWord)
+            {
+                candidate.push_back('a' + i);
+
+                if (candidate.length() > res.length() || (candidate.length() == res.length() && candidate < res))
+                    res = candidate;
+                
+                dfs(root->next[i], res, candidate);
+
+                candidate.pop_back();
+            }
+        }
+    }
+
+    void clear(TrieNode* root)
+    {
+        if (root == nullptr)
+            return ;
+
+        for (int i = 0; i < 26; ++i)
+            clear(root->next[i]);
+        delete root;
+    }
+};