首页 > 代码库 > LEETCODE--[leetcode] Regular Expression Matching

LEETCODE--[leetcode] Regular Expression Matching

http://blog.csdn.net/liyi_/article/details/42736903

Implement regular expression matching with support for ‘.‘ and ‘*‘.

‘.‘ Matches any single character.‘*‘ Matches zero or more of the preceding element.The matching should cover the entire input string (not partial).The function prototype should be:bool isMatch(const char *s, const char *p)Some examples:isMatch("aa","a") → falseisMatch("aa","aa") → trueisMatch("aaa","aa") → falseisMatch("aa", "a*") → trueisMatch("aa", ".*") → trueisMatch("ab", ".*") → trueisMatch("aab", "c*a*b") → true

 

solution: DP method. there are three main cases:

1. when *(p+1) == ‘*‘

      a. omitting ‘*‘ the preceding elements, considering the subsequent elements.

      b. if a doesn‘t work, pick ‘*‘ and preceding elements.

2. when *(p+1) != ‘*‘

3. else mismatch

bool isMatch(const char* s, const char* p) {    if(s == NULL || p == NULL) 
     return false; if(*p == \0 && *s == \0) return true; else { if( *(p+1) == * ) { if((*s != \0 && *p == .) || *s == *p) { //there may be zero or more preceding elements //we should take into account e.g: aaa-->a*a; aaa-->a*aa if(isMatch(s, p+2)) return true; return isMatch(++s, p); } else { return isMatch(s, p+2); } } else { if(*s == *p || (*s != \0 && *p == .)) { return isMatch(++s, ++p); } } return false; }}

 

LEETCODE--[leetcode] Regular Expression Matching