#include <stdbool.h>
#include<stdio.h>
#include<stdlib.h>
struct stack {
char val;
struct stack *next;
};
struct stack *top;
struct stack *init() {
struct stack *head = malloc(sizeof(struct stack));
head->next = NULL;
head->val = '\0';
return head;
}
void push(char val) {
struct stack *p = malloc(sizeof(struct stack));
p->val = val;
p->next = top;
top = p;
}
char pop() {
struct stack *p = top;
if (p->val == '\0') return '\0';
char ret = p->val;
top = top->next;
free(p);
return ret;
}
bool isValid(char *s) {
top = init();
int i = 0;
char p = s[i];
while (p != '\0') {
if (p == '(' || p == '{' || p == '[') {
push(p);
} else if (p == ')' || p == '}' || p == ']') {
if (p == ')' && pop(top) != '(') return false;
if (p == '}' && pop(top) != '{') return false;
if (p == ']' && pop(top) != '[') return false;
}
i++;
p = s[i];
}
if (top->val != '\0') return false;
while (top != NULL) {
struct stack *p = top;
top = top->next;
free(p);
}
return true;
}
int main() {
const char *s = "()[]{}[";
bool res = isValid(s);
printf("%s \t %d\n", s, res);
return 0;
}
class MyQueue(object):
def __init__(self):
self.s1=[]
self.s2=[]
def push(self, x):
"""
:type x: int
:rtype: None
"""
self.s1.append(x)
def pop(self):
"""
:rtype: int
"""
if not self.s1 and not self.s2:
return None
if self.s2:
return self.s2.pop()
while(self.s1):
self.s2.append(self.s1.pop())
return self.s2.pop()
def peek(self):
"""
:rtype: int
"""
if self.s2:
return self.s2[len(self.s2)-1]
while(self.s1):
self.s2.append(self.s1.pop())
return self.s2[len(self.s2)-1]
def empty(self):
"""
:rtype: bool
"""
return not self.s1 and not self.s2
