3138 stack Exercises 2, exercises 2

3138 stack Exercises 2, exercises 2
3138 stack Exercise 2

 

Time Limit: 1 s space limit: 128000 KB title level: Gold Question View running resultsDescription Description

(Compared with Stack Exercise 1, this question is changed to two places: 1. Enhanced Data. 2. There is no guarantee that the stack will not go out of the stack when the stack is empty)

Given a stack (initially empty, element type is integer, and smaller than or equal to 100), there are only two operations: inbound and outbound. First, these operations are provided. Please output the stack top element of the final stack. Operation explanation: 1 indicates inbound stack, 2 indicates outbound Stack

Input description Input Description

N (number of operations)

N operations (if it is an inbound stack, there will be an inbound stack element)

For details, see the example (the input does not guarantee that the stack will not go out of the stack when the stack is empty)

Output description Output Description

The final stack top element outputs "impossible!" If the final stack is empty or the stack is empty !" (Without quotation marks)

Sample Input Sample Input

3

1 2

2

2

Sample output Sample Output

Impossible!

Data range and prompt Data Size & Hint

For 100% of data, elements N ≤ 100000 are positive integers and smaller than or equal to 10 ^ 8

 

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 1 #include<iostream> 2 using namespace std; 3 int stack[100000001]; 4 int top=1; 5 int main() 6 { 7     int n; 8     cin>>n; 9     for(int i=1;i<=n;i++)10     {11         int a;12         cin>>a;13         if(a==2)14         {15             if(top==1)16             {17                 cout<<"impossible!";18                 return 0;19             }20             else21             {22                 top--;23             }24         }25         else26         {27             int b;28             cin>>b;29             stack[top]=b;30             top++;31         }32     }33     if(top==1)34     {35         cout<<"impossible!";36     }37     else38     {39         cout<<stack[top-1];40     }41     return 0;42 }