给定一堆整数。我们的任务是设计一个特殊的堆栈，以便可以在O(1)时间和O(1)额外空间中找到最大元素。
例子：
Given Stack :
2
5
1
64 --> Maximum
So Output must be 64 when getMax() is called.
下面是设计用来从堆栈中压入和弹出元素的不同功能。
Push(x) ：在堆栈顶部插入x。
- 如果堆栈为空，则将x插入堆栈，并使maxEle等于x。
- 如果堆栈不为空，则将x与maxEle进行比较。出现两种情况：
- 如果x小于或等于maxEle，只需插入x。
- 如果x大于maxEle，则将(2 * x – maxEle)插入堆栈，并使maxEle等于x。例如，让先前的maxEle为3。现在我们要插入4。我们将maxEle更新为4，然后将2 * 4 – 3 = 5插入堆栈。
Pop()：从堆栈顶部删除一个元素。
- 从顶部删除元素。令移除的元素为y。出现两种情况：
- 如果y小于或等于maxEle，则堆栈中的最大元素仍为maxEle。
- 如果y大于maxEle，则最大元素现在变为(2 * maxEle – y)，因此进行更新(maxEle = 2 * maxEle – y)。在这里，我们从当前最大值及其堆栈中的值中检索先前的最大值。例如，让要删除的元素为5，maxEle为4。我们删除5并将maxEle更新为2 * 4 – 5 = 3。
重要事项：
- 如果到目前为止，堆栈不保存元素的实际值。
- 实际的最大元素始终存储在maxEle中
插图
推(x)
- 要插入的数字：3，堆栈为空，因此将3插入堆栈，并且maxEle = 3。
- 要插入的数字：5，堆栈不为空，5> maxEle，将(2 * 5-3)插入堆栈，maxEle = 5。
- 要插入的数字：2，堆栈不为空，2
- 要插入的数字：1，堆栈不为空，1
- 要插入的数字：1，堆栈不为空，1
流行音乐()
- 最初，堆栈中的最大元素maxEle为5。
- 删除的数字：1，因为1小于maxEle，所以仅弹出1。maxEle = 5。
- 删除的数字：2、2
- 删除的数字：7、7> maxEle，原始数字为maxEle，即5，新的maxEle = 2 * 5 – 7 = 3。
C++
// C++ program to implement a stack that supports
// getMaximum() in O(1) time and O(1) extra space.
#include
using namespace std;
// A user defined stack that supports getMax() in
// addition to push() and pop()
struct MyStack {
stack s;
int maxEle;
// Prints maximum element of MyStack
void getMax()
{
if (s.empty())
cout << "Stack is empty\n";
// variable maxEle stores the maximum element
// in the stack.
else
cout << "Maximum Element in the stack is: "
<< maxEle << "\n";
}
// Prints top element of MyStack
void peek()
{
if (s.empty()) {
cout << "Stack is empty ";
return;
}
int t = s.top(); // Top element.
cout << "Top Most Element is: ";
// If t < maxEle means maxEle stores
// value of t.
(t > maxEle) ? cout << maxEle : cout << t;
}
// Remove the top element from MyStack
void pop()
{
if (s.empty()) {
cout << "Stack is empty\n";
return;
}
cout << "Top Most Element Removed: ";
int t = s.top();
s.pop();
// Maximum will change as the maximum element
// of the stack is being removed.
if (t > maxEle) {
cout << maxEle << "\n";
maxEle = 2 * maxEle - t;
}
else
cout << t << "\n";
}
// Removes top element from MyStack
void push(int x)
{
// Insert new number into the stack
if (s.empty()) {
maxEle = x;
s.push(x);
cout << "Number Inserted: " << x << "\n";
return;
}
// If new number is less than maxEle
if (x > maxEle) {
s.push(2 * x - maxEle);
maxEle = x;
}
else
s.push(x);
cout << "Number Inserted: " << x << "\n";
}
};
// Driver Code
int main()
{
MyStack s;
s.push(3);
s.push(5);
s.getMax();
s.push(7);
s.push(19);
s.getMax();
s.pop();
s.getMax();
s.pop();
s.peek();
return 0;
} Java
// Java program to implement a stack that supports
// getMaximum() in O(1) time and O(1) extra space.
import java.util.*;
class GFG
{
// A user defined stack that supports getMax() in
// addition to push() and pop()
static class MyStack
{
Stack s = new Stack();
int maxEle;
// Prints maximum element of MyStack
void getMax()
{
if (s.empty())
System.out.print("Stack is empty\n");
// variable maxEle stores the maximum element
// in the stack.
else
System.out.print("Maximum Element in" +
"the stack is: "+maxEle + "\n");
}
// Prints top element of MyStack
void peek()
{
if (s.empty())
{
System.out.print("Stack is empty ");
return;
}
int t = s.peek(); // Top element.
System.out.print("Top Most Element is: ");
// If t < maxEle means maxEle stores
// value of t.
if(t > maxEle)
System.out.print(maxEle);
else
System.out.print(t);
}
// Remove the top element from MyStack
void pop()
{
if (s.empty())
{
System.out.print("Stack is empty\n");
return;
}
System.out.print("Top Most Element Removed: ");
int t = s.peek();
s.pop();
// Maximum will change as the maximum element
// of the stack is being removed.
if (t > maxEle)
{
System.out.print(maxEle + "\n");
maxEle = 2 * maxEle - t;
}
else
System.out.print(t + "\n");
}
// Removes top element from MyStack
void push(int x)
{
// Insert new number into the stack
if (s.empty())
{
maxEle = x;
s.push(x);
System.out.print("Number Inserted: " + x + "\n");
return;
}
// If new number is less than maxEle
if (x > maxEle)
{
s.push(2 * x - maxEle);
maxEle = x;
}
else
s.push(x);
System.out.print("Number Inserted: " + x + "\n");
}
};
// Driver Code
public static void main(String[] args)
{
MyStack s = new MyStack();
s.push(3);
s.push(5);
s.getMax();
s.push(7);
s.push(19);
s.getMax();
s.pop();
s.getMax();
s.pop();
s.peek();
}
}
/* This code contributed by PrinciRaj1992 */ Python 3
# Class to make a Node
class Node:
#Constructor which assign argument to nade's value
def __init__(self, value):
self.value = value
self.next = None
# This method returns the string representation of the object.
def __str__(self):
return "Node({})".format(self.value)
# __repr__ is same as __str__
__repr__ = __str__
class Stack:
# Stack Constructor initialise top of stack and counter.
def __init__(self):
self.top = None
self.count = 0
self.maximum = None
#This method returns the string representation of the object (stack).
def __str__(self):
temp=self.top
out=[]
while temp:
out.append(str(temp.value))
temp=temp.next
out='\n'.join(out)
return ('Top {} \n\nStack :\n{}'.format(self.top,out))
# __repr__ is same as __str__
__repr__=__str__
#This method is used to get minimum element of stack
def getMax(self):
if self.top is None:
return "Stack is empty"
else:
print("Maximum Element in the stack is: {}" .format(self.maximum))
# Method to check if Stack is Empty or not
def isEmpty(self):
# If top equals to None then stack is empty
if self.top == None:
return True
else:
# If top not equal to None then stack is empty
return False
# This method returns length of stack
def __len__(self):
self.count = 0
tempNode = self.top
while tempNode:
tempNode = tempNode.next
self.count+=1
return self.count
# This method returns top of stack
def peek(self):
if self.top is None:
print ("Stack is empty")
else:
if self.top.value > self.maximum:
print("Top Most Element is: {}" .format(self.maximum))
else:
print("Top Most Element is: {}" .format(self.top.value))
#This method is used to add node to stack
def push(self,value):
if self.top is None:
self.top = Node(value)
self.maximum = value
elif value > self.maximum :
temp = (2 * value) - self.maximum
new_node = Node(temp)
new_node.next = self.top
self.top = new_node
self.maximum = value
else:
new_node = Node(value)
new_node.next = self.top
self.top = new_node
print("Number Inserted: {}" .format(value))
#This method is used to pop top of stack
def pop(self):
if self.top is None:
print( "Stack is empty")
else:
removedNode = self.top.value
self.top = self.top.next
if removedNode > self.maximum:
print ("Top Most Element Removed :{} " .format(self.maximum))
self.maximum = ( ( 2 * self.maximum ) - removedNode )
else:
print ("Top Most Element Removed : {}" .format(removedNode))
# Driver program to test above class
stack = Stack()
stack.push(3)
stack.push(5)
stack.getMax()
stack.push(7)
stack.push(19)
stack.getMax()
stack.pop()
stack.getMax()
stack.pop()
stack.peek()
# This code is contributed by BlinkiiC#
// C# program to implement a stack that supports
// getMaximum() in O(1) time and O(1) extra space.
using System;
using System.Collections.Generic;
class GFG
{
// A user defined stack that supports getMax() in
// addition to push() and pop()
public class MyStack
{
public Stack s = new Stack();
public int maxEle;
// Prints maximum element of MyStack
public void getMax()
{
if (s.Count == 0)
Console.Write("Stack is empty\n");
// variable maxEle stores the maximum element
// in the stack.
else
Console.Write("Maximum Element in" +
"the stack is: "+maxEle + "\n");
}
// Prints top element of MyStack
public void peek()
{
if (s.Count == 0)
{
Console.Write("Stack is empty ");
return;
}
int t = s.Peek(); // Top element.
Console.Write("Top Most Element is: ");
// If t < maxEle means maxEle stores
// value of t.
if(t > maxEle)
Console.Write(maxEle);
else
Console.Write(t);
}
// Remove the top element from MyStack
public void pop()
{
if (s.Count == 0)
{
Console.Write("Stack is empty\n");
return;
}
Console.Write("Top Most Element Removed: ");
int t = s.Peek();
s.Pop();
// Maximum will change as the maximum element
// of the stack is being removed.
if (t > maxEle)
{
Console.Write(maxEle + "\n");
maxEle = 2 * maxEle - t;
}
else
Console.Write(t + "\n");
}
// Removes top element from MyStack
public void push(int x)
{
// Insert new number into the stack
if (s.Count == 0)
{
maxEle = x;
s.Push(x);
Console.Write("Number Inserted: " + x + "\n");
return;
}
// If new number is less than maxEle
if (x > maxEle)
{
s.Push(2 * x - maxEle);
maxEle = x;
}
else
s.Push(x);
Console.Write("Number Inserted: " + x + "\n");
}
};
// Driver Code
public static void Main(String[] args)
{
MyStack s = new MyStack();
s.push(3);
s.push(5);
s.getMax();
s.push(7);
s.push(19);
s.getMax();
s.pop();
s.getMax();
s.pop();
s.peek();
}
}
// This code is contributed by Princi Singh 输出：
Number Inserted: 3
Number Inserted: 5
Maximum Element in the stack is: 5
Number Inserted: 7
Number Inserted: 19
Maximum Element in the stack is: 19
Top Most Element Removed: 19
Maximum Element in the stack is: 7
Top Most Element Removed: 7
Top Most Element is: 5