3139 stack exercises 3, exercises 3

3139 stack exercises 3, exercises 3
3139 stack Exercise 3

 

Time Limit: 2 s space limit: 128000 KB title level: Gold Question View running resultsDescription Description

Compared with the first question, this question adds another operation, accessing the top element of the stack (number 3, to ensure that the stack is not empty when accessing the top element of the stack or when the stack is out ), now the N operation is given, and the output result is.

Input description Input Description

N

N operations (1 in the stack, 2 out of the stack, 3 in the top of the stack)

Output description Output Description

Result of each K row (K is the number of queries in the input)

Sample Input Sample Input

6

1 7

3

2

1 9

1 7

3

Sample output Sample Output

7

7

Data range and prompt Data Size & Hint

For 50% of data, N ≤ 1000 of the inbound stack elements ≤ 200

For 100% of data, N ≤ 100000 of the inbound stack elements are positive integers and smaller than or equal to 10 ^ 4

CATEGORY tag Tags click here to expand

 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         else if(a==1)26         {27             int b;28             cin>>b;29             stack[top]=b;30             top++;31         }32         else if(a==3)33         {34             cout<<stack[top-1]<<endl;35         }36     }37 /*    if(top==1)38     {39         cout<<"impossible!";40     }41     else42     {43         cout<<stack[top-1];44     }*/45     return 0;46 }