LeetCode Regular Expression Matching

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class Solution {#define SINGLE 1#define MULTIP 2public:    bool isMatch(const char *s, const char *p) {        if (s == NULL || p == NULL) return true;                vector<pair<char, int> > pattern;                int     pos = 0;        char     ch = ‘\0‘;                while ((ch = p[pos++]) != ‘\0‘) {            if (ch == ‘*‘) {                pattern.back().second = MULTIP;                continue;            }            pattern.push_back(make_pair(ch, SINGLE));        }                return isMatch(s, 0, pattern, 0);    }        bool isMatch(const char *s, int pos, vector<pair<char, int> > &pattern, int ppos) {        if (ppos == pattern.size()) {            return s[pos] == ‘\0‘;        }        int i = pos;        pair<char, int> &p = pattern[ppos];        int     offset = (p.second == SINGLE) ? 0 : -1;        char     ch = ‘\0‘;        while (offset < 0 || (ch = s[pos + offset]) != ‘\0‘) {            if (offset >= 0 && !cmp(ch, p.first)) {                return false;            }            if (isMatch(s, pos + offset + 1, pattern, ppos + 1)) {                return true;            }            if (p.second == SINGLE) break;            offset++;        }        return false;    }        bool cmp(const char a, const char b) {        if (a == ‘.‘ || b == ‘.‘) return true;        return a == b;    }};

暴力法, 216ms,

 

 

改寫為記憶搜尋,這裡假設字串和模式字串的長度都不超過unsigned short 範圍(6w+)， 84ms

class Solution {#define SINGLE 1#define MULTIP 2private:    unordered_map<unsigned int, bool> memo;public:    bool isMatch(const char *s, const char *p) {        if (s == NULL || p == NULL) return true;        memo.clear();                vector<pair<char, int> > pattern;                int     pos = 0;        char     ch = ‘\0‘;                while ((ch = p[pos++]) != ‘\0‘) {            if (ch == ‘*‘) {                pattern.back().second = MULTIP;                continue;            }            pattern.push_back(make_pair(ch, SINGLE));        }                return isMatch(s, 0, pattern, 0);    }        bool isMatch(const char *s, int pos, vector<pair<char, int> > &pattern, int ppos) {        unsigned int id = (pos << 16) | ppos;                unordered_map<unsigned int, bool>::iterator iter = memo.find(id);        if (memo.find(id) != memo.end()) return iter->second;                bool res = false;                if (ppos == pattern.size()) {            res = s[pos] == ‘\0‘;            memo.insert(make_pair(id, res));            return res;        }        int i = pos;        pair<char, int> &p = pattern[ppos];        int     offset = (p.second == SINGLE) ? 0 : -1;        char     ch = ‘\0‘;        while (offset < 0 || (ch = s[pos + offset]) != ‘\0‘) {            if (offset >= 0 && !cmp(ch, p.first)) {                res = false;                break;            }            if (isMatch(s, pos + offset + 1, pattern, ppos + 1)) {                res = true;                break;            }            if (p.second == SINGLE) break;            offset++;        }        memo.insert(make_pair(id, res));        return res;    }        bool cmp(const char a, const char b) {        if (a == ‘.‘ || b == ‘.‘) return true;        return a == b;    }};

 

LeetCode Regular Expression Matching