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regex.c
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regex.c
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#include "regex.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "stack.h"
// Function Definitions
RegExp *createRegExp(char *pattern)
{
RegExp *regex = (RegExp *)malloc(sizeof(RegExp));
if (!regex)
return NULL;
regex->pattern = (char *)malloc(strlen(pattern));
if (!regex->pattern)
{
// Free regex first!
free(regex);
return NULL;
}
strcpy(regex->pattern, pattern);
return regex;
}
void deleteRegExp(RegExp *regex)
{
if (!regex)
return;
if (regex->pattern)
free(regex->pattern);
free(regex);
}
typedef struct
{
int i;
int pointer;
char ch;
char opr;
int length;
} _RegExpOpr;
// . + *
int matchRegExp(RegExp *regex, char *test)
{
// When match or pattern char is a dot, increment i and pointer and proceed.
// When pattern char is a plus or star, decrement pointer (if pointer is negative, return 0), create entry on stack, then:
// 1. if the created entry has a -1 (starting), then increment pointer until a different character is encountered, and note the length. Increment i and proceed.
// 2. if the created entry has a non-negative value, then decrement the pointer and add the value to the pointer, and proceed.
// 3. if the length is 0 for a star opr, or -1 (not starting) for star, pop the item from the stack and repeat the rule. If the stack is empty, return 0.
// When mismatch:
// 1. If the next pattern char is a star, simply increment i twice and proceed.
// 2. Else, backtrack to the top of the stack (copy values), and repeat same steps as when the pattern char is a plus or star.
// 3. If stack is empty, return 0.
// When null character of the test is encountered and pattern still has characters, treat as mismatch.
// When null character of the pattern is encountered and test still has characters, return 0.
// When both pattern char and test char is a null char, return 1.
Stack *stack = createStack();
if (!stack)
return -1;
int i = 0, pointer = 0;
int copyStackTop = 0;
int status = 1;
while (regex->pattern[i] != '\0' || test[pointer] != '\0')
{
if (copyStackTop) // Backtrack/Copy
{
int mustContinue = 0;
if (!stack->length)
{
status = 0;
break;
}
_RegExpOpr *data;
if (!popStack(stack, (void **)&data))
{
status = -2;
break;
}
i = data->i;
pointer = data->pointer;
if (data->length == -1)
{
if (copyStackTop == 1) // Starting
{
int length = 1;
pointer++;
while (test[pointer] == data->ch || data->ch == '.' && test[pointer] != '\0')
{
pointer++;
length++;
}
if (length == 1 && test[pointer] == '\0' && data->opr == '+')
{
status = 1;
break;
}
data->length = length;
i++;
mustContinue = 1;
}
else
{
status = 0;
break;
}
}
else
{
data->length--;
if ((data->length == 0 && data->opr == '+') || (data->length == -1 && data->opr == '*'))
{
deleteStackData(data);
continue;
}
pointer += data->length;
i++;
}
if (pushStack(stack, data, sizeof(_RegExpOpr)) != 0)
{
status = -2;
break;
}
copyStackTop = 0;
if (mustContinue)
continue;
}
if (regex->pattern[i] == '+' || regex->pattern[i] == '*') // Plus or Star
{
if (--pointer < 0)
{
status = 0;
break;
}
_RegExpOpr entry;
entry.i = i;
entry.pointer = pointer;
if (i - 1 < 0)
{
status = 0;
break;
}
entry.ch = regex->pattern[i - 1];
entry.opr = regex->pattern[i];
entry.length = -1;
if (pushStack(stack, &entry, sizeof(_RegExpOpr)) != 0)
{
status = -2;
break;
}
copyStackTop = 1;
}
else if (regex->pattern[i] == test[pointer] || regex->pattern[i] == '.' && test[pointer] != '\0') // Match
{
i++;
pointer++;
}
else if (regex->pattern[i] != test[pointer] || (test[pointer] == '\0' && regex->pattern[i] != '\0')) // Mismatch
{
if (regex->pattern[i + 1] == '*')
{
i += 2;
continue;
}
copyStackTop = 2;
continue;
}
else if (regex->pattern[i] == '\0' && test[pointer] != '\0') // Pattern end
{
status = 0;
break;
}
}
deleteStack(stack);
return status;
}