# Program: HackerRank stack problem - Equal Stacks.

 Problem Description: Problem Reference: Equal Stacks You have three stacks of cylinders where each cylinder has the same diameter, but they may vary in height. You can change the height of a stack by removing and discarding its topmost cylinder any number of times. Find the maximum possible height of the stacks such that all of the stacks are exactly the same height. This means you must remove zero or more cylinders from the top of zero or more of the three stacks until they're all the same height, then print the height. The removals must be performed in such a way as to maximize the height. Note: An empty stack is still a stack. Input Format The first line contains three space-separated integers, n1, n2, and n3, describing the respective number of cylinders in stacks 1, 2, and 3. The subsequent lines describe the respective heights of each cylinder in a stack from top to bottom: The second line contains n1 space-separated integers describing the cylinder heights in stack 1. The first element is the top of the stack. The third line contains n2 space-separated integers describing the cylinder heights in stack 2. The first element is the top of the stack. The fourth line contains n3 space-separated integers describing the cylinder heights in stack 3. The first element is the top of the stack. Output Format Print a single integer denoting the maximum height at which all stacks will be of equal height. Sample Input ```5 3 4 3 2 1 1 1 4 3 2 1 1 4 1``` Sample Output `5` Explanation Initially, the stacks look like this: Observe that the three stacks are not all the same height. To make all stacks of equal height, we remove the first cylinder from stacks 1 and 2, and then remove the top two cylinders from stack 3 (shown below). As a result, the stacks undergo the following change in height: 8 - 3 = 5 9 - 4 = 5 7 - 1 - 1 = 5 All three stacks now have height = 5. Thus, we print 5 as our answer. Our Approach 1) Keep track of stack heights indivitually. 2) Keep track of smallest stack height. 3) Continue removing from stacks until we reach the height of the smallest stack. 4) We can adjust the height of stack only by deletion to reach the smallest. Recalculate the smallest stack height at every step.

 EqualStacks ```package com.java2novice.algos; import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; import java.util.Scanner; import java.util.Stack; public class EqualStacks { static int equalStacks(int[] ha1, int[] ha2, int[] ha3) { Stack s1 = new Stack(); //First stack of cylinders Stack s2 = new Stack(); //Second stack of cylinders Stack s3 = new Stack(); //Third stack of cylinders int h1 = 0; //Height of the first stack int h2 = 0; //Height of the second stack int h3 = 0; //Height of the third stack int minStack; //The stack with the smallest height //Initialize the stacks and their heights for(int i = ha1.length-1; i >= 0 ; i--){ s1.push(ha1[i]); h1 += ha1[i]; } for(int i = ha2.length-1; i >= 0 ; i--){ s2.push(ha2[i]); h2 += ha2[i]; } for(int i = ha3.length-1; i >= 0 ; i--){ s3.push(ha3[i]); h3 += ha3[i]; } minStack = Math.min(h1,Math.min(h2,h3)); //Initialize minStack with the minimum height //Heights are not all equal enter the while loop while(h1 != h2 || h1 != h3) { //Remove cylinders from stack 1 until your height is <= the smallest while(h1 > minStack){ h1 -= s1.pop(); } minStack = Math.min(h1,Math.min(h2,h3)); //Recalculate min //Remove cylinders from stack 2 until your height is <= the smallest while(h2 > minStack){ h2 -= s2.pop(); } minStack = Math.min(h1,Math.min(h2,h3)); //Recalculate min //Remove cylinders from stack 3 until your height is <= the smallest while(h3 > minStack){ h3 -= s3.pop(); } minStack = Math.min(h1,Math.min(h2,h3)); //Recalculate min } return minStack; } private static final Scanner scanner = new Scanner(System.in); public static void main(String[] args) throws IOException { String[] n1N2N3 = scanner.nextLine().split(" "); int n1 = Integer.parseInt(n1N2N3[0].trim()); int n2 = Integer.parseInt(n1N2N3[1].trim()); int n3 = Integer.parseInt(n1N2N3[2].trim()); int[] h1 = new int[n1]; String[] h1Items = scanner.nextLine().split(" "); for (int h1Itr = 0; h1Itr < n1; h1Itr++) { int h1Item = Integer.parseInt(h1Items[h1Itr].trim()); h1[h1Itr] = h1Item; } int[] h2 = new int[n2]; String[] h2Items = scanner.nextLine().split(" "); for (int h2Itr = 0; h2Itr < n2; h2Itr++) { int h2Item = Integer.parseInt(h2Items[h2Itr].trim()); h2[h2Itr] = h2Item; } int[] h3 = new int[n3]; String[] h3Items = scanner.nextLine().split(" "); for (int h3Itr = 0; h3Itr < n3; h3Itr++) { int h3Item = Integer.parseInt(h3Items[h3Itr].trim()); h3[h3Itr] = h3Item; } int result = equalStacks(h1, h2, h3); System.out.println(result); } } ```

 Output: ```5 3 4 3 2 1 1 1 4 3 2 1 1 4 1 5```