leetcode-648. Replace Words

考察點：trie樹，指針；
思路：根據dict生成trie樹，判斷是否是_is_end時需要留意。

C++代碼：

class Solution {
public:
    struct TrieNode{
        bool _is_end;
        TrieNode * next[26];
        TrieNode(){
            _is_end = false;
            for (int i=0; i<26; i++) {
                next[i] = NULL;
            }
        };
    };

    TrieNode * root;

    void init(vector<string> & dict) {
        root = new TrieNode();
        TrieNode * temp=NULL;
        for (int i=0; i<dict.size(); i++) {
            temp = root;
            for (int j=0; j<dict[i].size(); j++) {
                int index = dict[i][j] - 'a';
                if (temp->next[index] == NULL) {
                    temp->next[index] = new TrieNode();
                }
                temp = temp->next[index];
            }
            temp->_is_end = true;
        }
    }

    vector<string> split_str(string sentence) {
        vector<string> ret;
        while(true) {
            int index = sentence.find(' ');
            if (index == string::npos) {
                ret.push_back(sentence);
                break;
            }
            ret.push_back(sentence.substr(0,index));
            sentence = sentence.substr(index+1);
        }
        return ret;
    }

    string process(string word) {
        int size = word.size();
        TrieNode * temp = root;
        for (int i=0; i<size; i++) {
            int index = word[i] - 'a';
            if (temp->next[index] == NULL) {

                return word;
            } else if (temp->next[index]->_is_end==true) {
                return word.substr(0,i+1);
            }
            temp = temp->next[index];
        }
        return word;
    }

    void replace(vector<string>& words) {
        for(int i=0; i<words.size(); i++) {
            words[i] = process(words[i]);
        }
    }

    string get_result_str(vector<string> & words) {
        string ret;
        for (int i=0; i<words.size(); i++) {
            if(i == words.size() - 1) {
                ret += words[i];
            } else {
                ret += words[i] + " ";
            }
        }
        return ret;
    }

    string replaceWords(vector<string>& dict, string sentence) {
        init(dict);
        vector<string> words = split_str(sentence);
        replace(words);
        string ret = get_result_str(words);
        return ret;
    }
};