Solution.java

//Problem: https://www.hackerrank.com/challenges/equal-stacks
//Java 8
/*
Initial Thoughts: If we put the cylinders into stacks(queues) and keep track
                  of their heights then we can continue removing from
                  stacks until we reach the height of the smallest 
                  stack. The smallest stack will continue to change as
                  we go. The reason we aim for them all to be the height
                  of the smallest stack, is because the only action we 
                  can perform is deleltion, therefore we can't grow the
                  smallest to match the others, but rather have to shrink
                  to meet the smallest
                  
Time Complexity: O(n) //We must look at every element in the worst case //n = n1+n2+n3
Space Complexity: O(n) //After initialization our stacks take up n space //n = n1+n2+n3
*/
import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n1 = in.nextInt(); //Number of cylinders in first stack
        int n2 = in.nextInt(); //Number of cylinders in second stack
        int n3 = in.nextInt(); //Number of cylinders in third stack
        Queue<Integer> s1 = new LinkedList<Integer>(); //First stack of cylinders
        Queue<Integer> s2 = new LinkedList<Integer>(); //Second stack of cylinders
        Queue<Integer> s3 = new LinkedList<Integer>(); //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 = 0; i < n1; i++){
            int cylinder = in.nextInt();
            s1.add(cylinder);
            h1 += cylinder;
        }
        
        for(int i = 0; i < n2; i++){
            int cylinder = in.nextInt();
            s2.add(cylinder);
            h2 += cylinder;
        }
        
        for(int i = 0; i < n3; i++){
            int cylinder = in.nextInt();
            s3.add(cylinder);
            h3 += cylinder;
        }
        minStack = Math.min(h1,Math.min(h2,h3));//Initialize minStack with the minimum height
        
        while(h1 != h2 || h1 != h3)//Heights are not all equal
        {
            //Remove cylinders from stack 1 until your height is <= the smallest
            while(h1 > minStack)
            {
                h1 -= s1.remove();
            }
            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.remove();
            }
            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.remove();
            }
            minStack = Math.min(h1,Math.min(h2,h3)); //Recalculate min
        }
        System.out.println(minStack);//All stacks are equal so minStack represents their height
    }
}