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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
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