What should be the reason to get Wrong Answer in the UVa site for this program? [closed]

Question

Here you'll find the problem: http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=614

#include<iostream>
#include<stack>
#include<string>
#include<cstdio>

/*farnaws,C++,673,08/12/2012*/

using namespace std;


string verifier(string input_line)
{

    stack <char> braces;
    int flag=0, count_left_first_brace=0,count_left_third_brace=0;
    for(int i=0; i<input_line.size(); i++)
    {

        if(input_line[i]=='(' || input_line[i]=='[')
        {
            braces.push(input_line[i]);
            if(input_line[i]=='(')
            {       
                count_left_first_brace++;
            }
            else if(input_line[i]=='[')
            {
                count_left_third_brace++;
            }

        }
        else if(input_line[i]==')' || input_line[i]==']')
        {
            if(!(braces.empty()==true))
            {
                if((input_line[i]==')' && braces.top()=='(') || (input_line[i]==']' && braces.top()=='[') )
                {
                    braces.pop();   
                }

            }

            if(input_line[i]==')')
            {       
                count_left_first_brace--;
            }
            else if(input_line[i]==']')
            {
                count_left_third_brace--;
            }
        }

    }
    if((braces.size()==0 && count_left_third_brace>=0 && count_left_first_brace>=0) || input_line.empty())
    {
         return "Yes";      
    }
    else
    {   
        return "No";
    }

}
int main()
{

   char line[128];
   int limit;
   cin>>limit;
   getchar();
   for(int i=0; i<limit; i++)
   {
            cin.getline(line,sizeof(line));
            string str=line;
            cout<<verifier(str)<<endl;
   }

   return 0;


}

Answer 1

Here's a style review, with a glance at efficiency. Not going to check for correctness, as that's outside the scope of the site. I'll start from main.

char line[128];

Why not use an std::string here? You're creating one later anyway; using it directly and passing by const reference would not be any slower.

getchar();

Either use streams, or use C-style IO; don't mix the two. Besides, streams have a perfectly good function to do this.

cin.getline(line, sizeof(line));

Don't do this. Do this instead:

std::getline(std::cin, line); // here, line should be an std::string

I would also not have verifier return a string; instead:

std::cout << (verifier(str) ? "Yes" : "No") << '\n';

(You have no reason to flush here.)

Moving onto the verifier function itself. A range-based for loop would be much more convenient:

for (char c : input_line) {
    // logic
}

The flag variable is unused, as far as I can tell.

The if(!(braces.empty()==true)) could much better be written as

if (!braces.empty())

Your count_left_third_brace and count_right_third_brace variables are not necessary; you can determine whether the code is right based purely on the contents of the stack.

The function boils down to:

bool verifier(std::string const& str) {
    std::stack<char> braces;
    for (char c : str) {
        switch (c) {
            case '(':
            case '[':
                braces.push(c);
                break;
            case ')':
                if (braces.empty() || braces.top() != '(')
                    return false;
                braces.pop();
                break;
            case '[':
                if (braces.empty() || braces.top() != ']')
                    return false;
                braces.pop();
                break;
        }
    }
    return true;
}

This is mostly equivalent to the existing code, and is probably closer to the intent.