Explain how to implement two stacks in one array A[1..n] in such a way that neither stack overflows unless the total number of elements in both stacks together is n. The PUSH and POP operations should run in O(1) time.
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![Explain how to implement two stacks in one array A[1..n] in such a way that neither stack
overflows unless the total number of elements in both stacks together is n. The PUSH and POP
operations should run in O(1) time.
Justify your answer and give some examples.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F4a7c9404-2115-4e54-bc8c-344a84b8b863%2Fe7ead1d5-d28a-48eb-84c9-0d8028a77050%2F66z9z7f_processed.png&w=3840&q=75)
Answer:
->The purpose is to start two stacks from two extreme corners of arr[]/stack1 starts from the leftmost element, the first element in stack1 is pushed at index 0.
->The stack2 starts from the rightmost corner, the first element in stack2 is pushed at index(n-1). Both stacks grow in opposite direction.
->To check for overflow, all we need to check is for space between top elements of both stacks. This check is highlighted in the below code:
Programming Code:
import java.io.*;
import java.util.*;
class twoStacks
{
int *arr;
int size;
int tops1,top2;
public:
twoStacks(int n) //constructor
{
size=n;
arr= new int[n];
top1=-1;
top2= size;
}
//Method to push an element x to stack1
void push(intx)
{
//There is atleast one empty space for new element
if(top1<top2-1)
{
top1++;
arr[top1]=x;
}
else
{
System.out.println("Stack Overflow");
exit(1);
}
//Method to push an element x to stack2
void push2(int x)
{
//There is at least one empty space for new element
if(top1<top2-1)
{
top2--;
arr[top2]=x;
}
else
{
System.out.println("Stack Overflow");
exit(1);
}
}
//Method to pop an element from first stack
int pop1()
{
if(top1>=0)
{
int x=arr[top1];
top1..;
return x;
}
else
{
System.out.println("Stack underFlow");
exit(1);
}
}
//Method to pop an element from second stack
int pop2()
{
if(top2<size)
{
int x=arr[top2];
top2++;
return x;
}
else
{
System.out.println("Stack underFlow");
exit(1);
}
}
}
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