// Returns true iff regex matches a prefix of str. regex must be a
// valid simple regular expression and not start with "^", or the
// result is undefined.
bool MatchRegexAtHead(const char* regex, const char* str) {
if (*regex == '\0') // An empty regex matches a prefix of anything.
return true;
// "$" only matches the end of a string. Note that regex being
// valid guarantees that there's nothing after "$" in it.
if (*regex == '$')
return *str == '\0';
// Is the first thing in regex an escape sequence?
const bool escaped = *regex == '\\';
if (escaped)
++regex;
if (IsRepeat(regex[1])) {
// MatchRepetitionAndRegexAtHead() calls MatchRegexAtHead(), so
// here's an indirect recursion. It terminates as the regex gets
// shorter in each recursion.
return MatchRepetitionAndRegexAtHead(
escaped, regex[0], regex[1], regex + 2, str);
} else {
// regex isn't empty, isn't "$", and doesn't start with a
// repetition. We match the first atom of regex with the first
// character of str and recurse.
return (*str != '\0') && AtomMatchesChar(escaped, *regex, *str) &&
MatchRegexAtHead(regex + 1, str + 1);
}
}
// Generates non-fatal failures and returns false if regex is invalid;
// otherwise returns true.
bool ValidateRegex(const char* regex) {
if (regex == NULL) {
// TODO([email protected]): fix the source file location in the
// assertion failures to match where the regex is used in user
// code.
ADD_FAILURE() << "NULL is not a valid simple regular expression.";
return false;
}
bool is_valid = true;
// True iff ?, *, or + can follow the previous atom.
bool prev_repeatable = false;
for (int i = 0; regex[i]; i++) {
if (regex[i] == '\\') { // An escape sequence
i++;
if (regex[i] == '\0') {
ADD_FAILURE() << FormatRegexSyntaxError(regex, i - 1)
<< "'\\' cannot appear at the end.";
return false;
}
if (!IsValidEscape(regex[i])) {
ADD_FAILURE() << FormatRegexSyntaxError(regex, i - 1)
<< "invalid escape sequence \"\\" << regex[i] << "\".";
is_valid = false;
}
prev_repeatable = true;
} else { // Not an escape sequence.
const char ch = regex[i];
if (ch == '^' && i > 0) {
ADD_FAILURE() << FormatRegexSyntaxError(regex, i)
<< "'^' can only appear at the beginning.";
is_valid = false;
} else if (ch == '$' && regex[i + 1] != '\0') {
ADD_FAILURE() << FormatRegexSyntaxError(regex, i)
<< "'$' can only appear at the end.";
is_valid = false;
} else if (IsInSet(ch, "()[]{}|")) {
ADD_FAILURE() << FormatRegexSyntaxError(regex, i)
<< "'" << ch << "' is unsupported.";
is_valid = false;
} else if (IsRepeat(ch) && !prev_repeatable) {
ADD_FAILURE() << FormatRegexSyntaxError(regex, i)
<< "'" << ch << "' can only follow a repeatable token.";
is_valid = false;
}
prev_repeatable = !IsInSet(ch, "^$?*+");
}
}
return is_valid;
}
int main()
{
int chainLength = 0 ;
unsigned int num1 = 0, num2 = 0, diff = 0 ;
Str100 input, theBiggestNum, theSmallestNum ;
for( int i = 0 ; i < 100 ; i++ ) input[i] = theBiggestNum[i] = theSmallestNum[i] = '\0' ;
cin >> input ;
while( strcmp( input, "0" ) != 0 )
{
cout << "Original number was " << input << endl ;
while( !IsRepeat( diff ) )
{
FindBiggestAndSmallestNum( input, theBiggestNum, theSmallestNum ) ;
num1 = atoi( theBiggestNum ) ;
num2 = atoi( theSmallestNum ) ;
diff = num1 - num2 ;
cout << num1 << " - " << num2 << " = " << diff << endl ;
/*
sprintf是將數字轉成字串，中間的%u代表的是我的數字是unsigned int
*/
sprintf( input, "%u", diff ) ;
chainLength++ ;
} // while
cout << "Chain Length " << chainLength << "\n" << endl ;
/*
得到答案後，別忘記初始化
*/
gLastDiff = DEFALUT_DIFF ;
chainLength = 0 ;
cin >> input ;
} // while
return 0 ;
} // main()
