Coding: Create a stack with the usual push() & pop(), but with an additional function getMiddle() that returns the middle element of the stack in constant time.

Question

Harish · Accepted Answer

import os
import re
import sys

class Stack:
    def __init__(self):
        self.arrList = []
        
    def isEmpty(self):
        if len(self.arrList):
            return False
        else:
            return True
    
    def push(self, val):
        self.arrList.append(val)
        
    def pop(self):
        if not self.isEmpty():
            self.arrList[len(self.arrList)-1]
            self.arrList = self.arrList[:len(self.arrList)-1]
        else:
            print "Array list is empty"
            
    def returnMiddle(self):
        if not self.isEmpty():
            mid = len(self.arrList)/2
            return self.arrList[mid]
        else:
            print "Array list is empty"
            
    def listStack(self):
        print self.arrList
        
s = Stack()
s.push(5)
s.push(6)
s.listStack()
print s.returnMiddle()
s.pop()
s.listStack()
s.push(20)
s.push(45)
s.push(435)
s.push(35)
s.listStack()
print s.returnMiddle()
s.pop()
s.listStack()

Greeky · Answer

public int getNext(int[] ar, int k) {
        int low = 0;
        int high = ar.length-1;
        int mid = low+(high-low)/2;
        if (ar[high] k && (mid==0 || ar[mid-1]<=k)) {
                return ar[mid];
            }
            if(ar[mid]<=k) {
                low = mid+1;
            } else {
                high = mid;
            }
            mid = low+(high-low)/2;
        }
        return -1;
    }

Sruthi · Answer

public class CreateStack {

	List l = new LinkedList();
	public void push(Integer i)
	{
		l.add(i);
	}
	
	public void pop(){
		l.remove(l.size()-1);
	}
	
	public Integer getMiddle(){
		return l.get((l.size()-1)/2);
	}
	}

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