import java.util.ArrayList; import java.util.List; import java.util.Stack; publi

Question

import java.util.ArrayList; import java.util.List; import java.util.Stack; public class TowersOfHanoi { private int n; private List<Stack<Integer>> pegs; private boolean verbose; public TowersOfHanoi(int n, boolean verbose) { this.n = n; this.verbose = verbose; pegs = new ArrayList<>(); // each peg is represented by a stack for (int i = 0; i < 3; i++) pegs.add(new Stack<>()); // push disks onto peg 0, from biggest to smallest for (int i = n; i > 0; i--) pegs.get(0).push(i); } public void solve() { // TODO: solve the problem by making calls to moveTopDisk // Tip 1: you may find it helpful to break your code into multiple functions // Tip 2: start by running the code as is // Then add a single call to moveTopDisk to see what happens. // Hint: make an initial call to moveStack with the correct parameter values. // Then finish implementing moveStack. } public void moveStack(int n, int fromPeg, int toPeg) { int otherPeg = 3 - fromPeg - toPeg; // sum of the peg indices is 0 + 1 + 2 = 3 // finish this implementation } public void moveTopDisk(int fromPeg, int toPeg) { int disk = pegs.get(fromPeg).pop(); Stack<Integer> peg = pegs.get(toPeg); assert (peg.isEmpty() || peg.peek() > disk); // valid move peg.push(disk); if (verbose) System.out.println(this); } public String toString() { String s = ""; for (int i = n - 1; i >= 0; i--) { s += "| "; for (List<Integer> peg : pegs) { if (i < peg.size()) { int d = peg.get(i); s += space(n-d) + disk(2*d) + space(n-d); } else { s += space(2*n); } s += " | "; } s += " "; } return s; } public static String disk(int size) { String result = ""; for (int i = 0; i < size; i++) result += "="; return result; } public static String space(int size) { String result = ""; for (int i = 0; i < size; i++) result += " "; return result; } public static void main(String[] args) { TowersOfHanoi towers = new TowersOfHanoi(4, true); System.out.println(towers); towers.solve(); } } import java.util.ArrayList; import java.util.List; import java.util.Stack; public class TowersOfHanoi { private int n; private List<Stack<Integer>> pegs; private boolean verbose; public TowersOfHanoi(int n, boolean verbose) { this.n = n; this.verbose = verbose; pegs = new ArrayList<>(); // each peg is represented by a stack for (int i = 0; i < 3; i++) pegs.add(new Stack<>()); // push disks onto peg 0, from biggest to smallest for (int i = n; i > 0; i--) pegs.get(0).push(i); } public void solve() { // TODO: solve the problem by making calls to moveTopDisk // Tip 1: you may find it helpful to break your code into multiple functions // Tip 2: start by running the code as is // Then add a single call to moveTopDisk to see what happens. // Hint: make an initial call to moveStack with the correct parameter values. // Then finish implementing moveStack. } public void moveStack(int n, int fromPeg, int toPeg) { int otherPeg = 3 - fromPeg - toPeg; // sum of the peg indices is 0 + 1 + 2 = 3 // finish this implementation } public void moveTopDisk(int fromPeg, int toPeg) { int disk = pegs.get(fromPeg).pop(); Stack<Integer> peg = pegs.get(toPeg); assert (peg.isEmpty() || peg.peek() > disk); // valid move peg.push(disk); if (verbose) System.out.println(this); } public String toString() { String s = ""; for (int i = n - 1; i >= 0; i--) { s += "| "; for (List<Integer> peg : pegs) { if (i < peg.size()) { int d = peg.get(i); s += space(n-d) + disk(2*d) + space(n-d); } else { s += space(2*n); } s += " | "; } s += " "; } return s; } public static String disk(int size) { String result = ""; for (int i = 0; i < size; i++) result += "="; return result; } public static String space(int size) { String result = ""; for (int i = 0; i < size; i++) result += " "; return result; } public static void main(String[] args) { TowersOfHanoi towers = new TowersOfHanoi(4, true); System.out.println(towers); towers.solve(); } }

Explanation / Answer

Below is the implementation of the solve() function

public void solve() {

//Move the complete stack of 4 disks in 0th index to 2nd index by calling the function moveStack
   moveStack(4, 0, 2);

   }

Below is the implementation of the moveStack() function
public void moveStack(int n, int fromPeg, int toPeg) {

    //use other Peg for help while Moving
   int otherPeg = 3 - fromPeg - toPeg; // sum of the peg indices is 0 + 1 + 2 = 3
   // n = 1 means we just have to move single disk from fromPeg to toPeg
   if (n == 1)
    {
       moveTopDisk(fromPeg,toPeg);
        return;
    }

//First move the (n-1) disks from fromPeg to otherPeg
   moveStack(n-1, fromPeg, otherPeg);

//Then again move the (n-1) disks again from otherPeg to toPeg for arranging in correct order.
   moveStack(n-1, otherPeg, toPeg);
   }

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