[leetcode] Regular Expression Matching

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*aaif(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;}}