Regular Expression Matching
2014-06-07 17:54
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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") → false
isMatch("aa","aa") → true
isMatch("aaa","aa") → false
isMatch("aa", "a*") → true
isMatch("aa", ".*") → true
isMatch("ab", ".*") → true
isMatch("aab", "c*a*b") → true
首先明白匹配的规则,如c*表示0-n个c。所以根据匹配位置的下一位是否为*来做判断。通过递归来做,如果p到了末尾,就判断s是否在末尾就好。
如果p的下一位是*,就循环比较s和p的指向的值,如果相同,s++,原因如c*的解释。在循环中需要判断s与p+2的情况,也就是c*表示空的情况,是否成立。
如果p的下一位不是*,只需要判断当前s和p指向的值,不同就是false,相同递归判断s+1与p+1.
bool isMatch(const char *s, const char *p) {
if(*p == '\0')
return *s == '\0';
if(*(p+1) == '*'){
while(*s != '\0' && (*p == *s || *p == '.'))
if(isMatch(s, p+2))
return true;
else
s++;
return isMatch(s, p+2);
}else{
if(*s != '\0' && (*p == *s || *p == '.'))
return isMatch(s+1, p+1);
return false;
}
}
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