Answer to Question #158409 in C++ for shakib

Question

  

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

Open brackets must be closed by the same type of brackets.

Open brackets must be closed in the correct order.

Example 1:

Input: s = "()"

Output: true

Example 2:

Input: s = "()[]{}"

Output: true

Example 3:

Input: s = "(]"

Output: false

Example 4:

Input: s = "([)]"

Output: false

Example 5:

Input: s = "{[]}"

Output: true

*Your program output should follow the example in the instruction.

* The program should print the input parentheses and the output (true/false).                                                                     

*Parentheses.txt : ((()))

You are required to follow this program template I provide and use stack to solve the problem. Please test the program.

#include <stdio.h>

#include <stdlib.h>

// This is where the parentheses are stored in memory

char buffer[1024];

char stack_pop();

void stack_push(char ch);

int stack_size();

int main(){

FILE *fp;

  // The parentheses sequences is in the parentheses.txt file.

  fp=fopen("parentheses.txt","r");

  if(fp==NULL){

   printf("The input file does not exist.\n");

   exit(-1);

  }

  // Read the parenthese sequences into buffer array.

  fgets(buffer,1024,fp);

  //printf("%s",buffer);

}

// The pop operation in the stack. To be done.

char stack_pop(){

return ')';

}

// The push operation in the stack. To be done.

void stack_push(char ch){

}

// The number of elements in the stack. To be done.

int stack_size(){

return 0;

}

Answer 1

#include <iostream>
#include <stack>
#include <string> 
using namespace std;


int main(){
	string s;
	getline (cin, s);
	stack<char> st;
	
	for(int i = 0; i < s.size(); ++i)
	{
		if(s[i] == '(' || s[i] == '[' || s[i] == '{') st.push(s[i]);
		if(s[i] == ')' && st.top() == '(') 
		{
			st.pop();
			continue;
		}
		if(s[i] == ')' && st.top() != '(') 
		{
			cout << "No";
			return 0;
		}


		if(s[i] == ']' && st.top() == '[') 
		{
			st.pop();
			continue;
		}
		if(s[i] == ']' && st.top() != '[') 
		{ 
			cout << "No";
			return 0;
		}
		if(s[i] == '}' && st.top() == '{') 
		{
			st.pop();
			continue;
		}
		if(s[i] == '}' && st.top() != '{') 
		{ 
			cout<< "No";
			return 0;
		}
		
	}
	cout << endl;
	cout << s << endl;
	st.empty()? cout << "Yes" : cout << "No"; 
	cout << endl << "Press any char and press 'Enter' : ";
	cin >> s;
	return 0;
}