leetcode记录10. Regular Expression Matching

最新推荐文章于 2024-02-23 10:40:54 发布

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最新推荐文章于 2024-02-23 10:40:54 发布

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本文介绍了一种正则表达式匹配算法的实现，通过构建状态机的方式进行字符串与正则表达式的匹配，该算法在C++环境下运行效率较高，优于57.56%的在线提交。

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10. Regular Expression Matching

Runtime: 16 ms, faster than 57.56% of C++ online submissions for Regular Expression Matching.
Memory Usage: 11.5 MB, less than 56.12% of C++ online submissions for Regular Expression Matching.

class Solution {
public:
    bool isMatch(string s, string p) {
        if (p[0] == '*'){
            return true;
        }
     struct Node
    {
        char selfChar = ' ';
        char nextChar = ' ';
        bool flag = 0;
        Node* next = NULL;
        /* data */
    };
    vector<Node*> state;
    Node* startNode = new Node();
    Node* pNode = startNode;

    state.push_back(pNode);
    for(int i = 0; i < p.size(); i++)
    {
        if(i < p.size() - 1 && p[i+1] == '*')
        {
            pNode->selfChar = p[i];
            pNode->nextChar = ' ';
            Node* temp = new Node();
            pNode->next = temp;
            pNode = pNode->next;
            state.push_back(pNode);
            i += 1;
        }
        else
        {
            Node* temp = new Node();
            pNode->next = temp;
            pNode->nextChar = p[i];
            pNode = pNode->next;
            state.push_back(pNode);
        }
    }
    vector<vector<int>> first;
    for(int i = state.size()-1; i >= 0 ; i--)
    {
        vector<int> temp;
        if (state[i]->nextChar != ' ' || state[i]->next == NULL){
            temp.push_back(i);
            first.push_back(temp);
        }else{
            temp = first[first.size()-1];
            temp.push_back(i);
            first.push_back(temp);
        }
    }
    int len = first.size();
    reverse(first.begin(), first.end());
    set<int> match;
    for(int i = 0; i < first[0].size(); i++){
        match.insert(first[0][i]);
    }
    for(int i = 0; i < s.size(); i++)
    {
        vector<int> temp;
        set<int>::iterator iter;
        for(iter = match.begin(); iter != match.end(); iter++){
            if(state[*iter]->nextChar == s[i] || state[*iter]->nextChar == '.'){
                temp.insert(temp.end(), first[*iter+1].begin(), first[*iter+1].end());
            }else if(state[*iter]->selfChar == s[i] || state[*iter]->selfChar == '.'){
                temp.insert(temp.end(), first[*iter].begin(), first[*iter].end());
            }
        }
        match.clear();
        for(int j = 0; j < temp.size(); j++){
            match.insert(temp[j]);
        }
    }

    if (match.empty()) {
        return false;
    }else
    {
        if(match.find(len-1) != match.end()){
            return true;
        }else{
            return false;
        }

    }
    return 0;
    }
};