Parentheses Balance UVA 673

Parentheses Balance

You are given a string consisting of parentheses () and []. A string of this type is said to be correct:

(a)

if it is the empty string

(b)

if A and B are correct, AB is correct,

(c)

if A is correct,  (A ) and  [A ] is correct.

Write a program that takes a sequence of strings of this type and check their correctness. Your program can assume that the maximum string length is 128.

Input 

The file contains a positive integer  n  and a sequence of  n  strings of parentheses  ()  and  [] , one string a line.

Output 

A sequence of  Yes  or  No  on the output file.

Sample Input 

3
([])
(([()])))
([()[]()])()

Sample Output 

Yes
No
Yes

Miguel Revilla 
2000-08-14

一道符号匹配的问题，这类题是栈的典型应用了，比较简单，只需要注意一下各种情况不然很容易wrong answer

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

using namespace std;

int main()
{
    int n;
    cin>>n;
    string str1;
    getline(cin,str1);
    while(n--)
    {
        string str;
        stack<char> s;
        int i,flag=1;
        getline(cin,str);
        for(i=0;i<str.size();i++)
        {
            if(str[i]=='(')
            {
                s.push(str[i]);
            }
            else if(str[i]=='[')
            {
                s.push(str[i]);
            }
            else if(str[i]==')')
            {
                if(s.empty())
                {
                    flag=0;
                    break;
                }
                else if(s.top()!='(')
                {
                    flag=0;
                    break;
                }
                else
                {
                    s.pop();
                }
            }
            else if(str[i]==']')
            {
                if(s.empty())
                {
                    flag=0;
                    break;
                }
                else if(s.top()!='[')
                {
                    flag=0;
                    break;
                }
                else
                {
                    s.pop();
                }
            }
        }
        if(!s.empty()) flag=0;
        if(flag) cout<<"Yes"<<endl;
        else cout<<"No"<<endl;
    }
    return 0;
}