给定q个查询，您需要在堆栈上执行操作。查询有三种类型：1、2和3。如果操作是推动（1），则推动元素；如果操作是弹出（2），则弹出元素；如果是顶部（3），则在堆栈顶部打印元素（如果堆栈为空，则打印“-1”，不带引号）。 例如：
null
Input: Queries = 6 3 1 5 1 6 1 7 2 3Output: -1 6 The first query is to print top, but since the stack is empty, so we print -1.Next three queries are to push 5, 6, and 7, so we pushed them on a stack. Next query is pop, so we popped 7 from a stack. Final query is to print thetop, so 6 is there at the top and thus printed.
方法： 堆栈 可用于执行给定的操作。如果查询的输入为1，则获取另一个输入，并使用 推 作用如果查询的输入为2，则使用 这个 pop（） 在堆栈中运行。如果查询的输入为3，则使用 这个 top（） 作用 以下是上述方法的实施情况：
C++
// C++ program for // Sudo-Placement | Stack Design #include <bits/stdc++.h> using namespace std; stack< int > s; // function to perform type-1 operation void _push( int n) { s.push(n); } // function to perform type-2 operation void _pop() { s.pop(); } // function to perform type-3 operation void print() { // if the stack is not empty if (!s.empty()) cout << s.top() << endl; else cout << -1 << endl; } // Driver Code int main() { // 1st query print(); // 2nd query _push(5); // 3rd query _push(6); // 4th query _push(7); // 5th query _pop(); // 6th query print(); return 0; } |
JAVA
import java.util.*; // Java program for // Sudo-Placement | Stack Design class GFG { static Stack<Integer> s = new Stack<>(); // function to perform type-1 operation static void _push( int n) { s.push(n); } // function to perform type-2 operation static void _pop() { s.pop(); } // function to perform type-3 operation static void print() { // if the stack is not empty if (!s.empty()) { System.out.println(s.peek()); } else { System.out.println(- 1 ); } } // Driver Code public static void main(String[] args) { // 1st query print(); // 2nd query _push( 5 ); // 3rd query _push( 6 ); // 4th query _push( 7 ); // 5th query _pop(); // 6th query print(); } } // This code contributed by Rajput-Ji |
Python3
# Python3 program for # Sudo-Placement | Stack Design s = []; # function to perform # type-1 operation def _push(n): s.append(n); # function to perform # type-2 operation def _pop(): s.pop(); # function to perform # type-3 operation def _print(): # if the stack is not # empty if ( len (s) > 0 ): print (s[ len (s) - 1 ]); else : print ( "-1" ); # Driver Code if __name__ = = '__main__' : # 1st query _print(); # 2nd query _push( 5 ); # 3rd query _push( 6 ); # 4th query _push( 7 ); # 5th query _pop(); # 6th query _print(); # This code is contributed by 29AjayKumar |
C#
// C# program for // Sudo-Placement | Stack Design using System; using System.Collections.Generic; class GFG { static Stack< int > s = new Stack< int >(); // function to perform type-1 operation static void _push( int n) { s.Push(n); } // function to perform type-2 operation static void _pop() { s.Pop(); } // function to perform type-3 operation static void print() { // if the stack is not empty if (s.Count != 0) { Console.WriteLine(s.Peek()); } else { Console.WriteLine(-1); } } // Driver Code public static void Main() { // 1st query print(); // 2nd query _push(5); // 3rd query _push(6); // 4th query _push(7); // 5th query _pop(); // 6th query print(); } } /* This code contributed by PrinciRaj1992 */ |
Javascript
<script> // Javascript program for // Sudo-Placement | Stack Design let s=[]; // function to perform type-1 operation function _push(n) { s.push(n); } // function to perform type-2 operation function _pop() { s.pop(); } // function to perform type-3 operation function print() { // if the stack is not empty if (s.length!=0) { document.write(s[s.length-1]+ "<br>" ); } else { document.write(-1+ "<br>" ); } } // Driver Code // 1st query print(); // 2nd query _push(5); // 3rd query _push(6); // 4th query _push(7); // 5th query _pop(); // 6th query print(); // This code is contributed by rag2127 </script> |
输出：
-16
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