（Trie）LeetCode Weekly Contest 42 Q4 648. Replace Words

In English, we have a concept called root, which can be followed by some other words to form another longer word - let's call this word successor. For example, the root an, followed by other, which can form another word another.

Now, given a dictionary consisting of many roots and a sentence. You need to replace all the successor in the sentence with the rootforming it. If a successor has many roots can form it, replace it with the root with the shortest length.

You need to output the sentence after the replacement.

Example 1:

Input: dict = ["cat", "bat", "rat"]
sentence = "the cattle was rattled by the battery"
Output: "the cat was rat by the bat"

Note:

1. The input will only have lower-case letters.
2. 1 <= dict words number <= 1000
3. 1 <= sentence words number <= 1000
4. 1 <= root length <= 100
5. 1 <= sentence words length <= 1000

几乎可以说是裸的Trie。用dic中的单词建立字典树（注意字典树动态生成大小，直接开数组或map会MLE）。句子中的每个单词在字典树中按查询的方式走，遇到字典中某个单词的结尾就返回这个单词，遇到没有结点时就直接把该单词完整输出即可。 给出一行含空格的字符串还是直接用stringstream处理比较方便。

class Solution {
public:
    struct Trie {
        bool isWord;
        Trie* child[26];

        Trie(bool isWord) : isWord(isWord) {
            memset(child, 0, sizeof(child));
        }

        void addWord(string& s) {
            Trie* cur = this;
            for (char c : s) {
                Trie* next = cur->child[c - 'a'];
                if (next == nullptr) {
                    next = cur->child[c - 'a'] = new Trie(false);
                }
                cur = next;
            }
            cur->isWord = true;
        }

        ~Trie() {
            for (int i = 0; i < 26; ++i) {
                if (child[i]) {
                    delete child[i];
                }
            }
        }
    };
    string findRoot(Trie& root, string& s) {
        Trie* cur = &root;
        for (int i = 0; i < s.size(); ++i) {
            char c = s[i];
            cur = cur->child[c - 'a'];
            if (cur == nullptr) {
                return s;
            }
            if (cur->isWord) {
                return s.substr(0, i + 1);
            }
        }
        return s;
    }
    string replaceWords(vector<string>& dict, string sentence) {
        Trie tem(false);
        string res;
        for(int i=0;i<dict.size();i++)
        {
            tem.addWord(dict[i]);
        }
        stringstream ss(sentence);
        string s;
        while(ss>>s)
        {
            if(res.size())
                res+=" ";
            res+=findRoot(tem,s);
        }
        return res;
    }
};