2015 HUAS Summer Training#2~A

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 

Output 

Sample Input 

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

Sample Output 

Yes
No
Yes

解题思路：此题应该利用栈的特点来解，输入当碰到‘)‘或‘]‘时进行判断，看前面是不是与之配对的‘(‘及‘[‘，如果是就去掉栈顶元素，若不是就要将其放进去并且退出循环，注意每进行一次判断之前都要判断栈是否为空。如果用gets(); 对数组进行输入，那么在输入数字之后要用getchar();这是因为gets();对空格也吸收。还要注意题目要求，空格也输出，所以做题要小心。

程序代码：

#include<cstdio>
#include<stack>
using namespace std;

int main()
{
 int n,i;
 scanf("%d",&n);
 getchar();
 while(n--)
 {
  stack<char>s;
     char a[200];
  gets(a);
  int t=strlen(a);
  if(t==0)  {printf("Yes\n");continue;}  //用break;会使程序跳出去截止，就不会进行下一组了。
  char ch;
  for(i=0;i<t;i++)
        {
   if(a[i]==‘)‘)
   {
    if(s.empty())
    {
     s.push(a[i]);
     break;
    }
    ch=s.top();
    if(ch==‘[‘)
    break;
    s.pop();
   }
            else if(a[i]==‘]‘)
   {
    if(s.empty())
    {
     s.push(a[i]);
     break;
    }
    ch=s.top();
    if(ch==‘(‘)
    break;
    s.pop();
   }
   else
   s.push(a[i]);
  }
  if(s.empty())  printf("Yes\n");
   else printf("No\n");
 }
 return 0;
}