Data Structures and Algorithm Analysis - Computer Science at ...

124 Chap. 4 Lists, Stacks, and Queuespublic enum operation { MOVE, TOH }class TOHobj {public operation op;public int num;public Pole start, goal, temp;}/** Recursive call operation */TOHobj(operation o, int n, Pole s, Pole g, Pole t){ op = o; num = n; start = s; goal = g; temp = t; }/** MOVE operation */TOHobj(operation o, Pole s, Pole g){ op = o; start = s; goal = g; }static void TOH(int n, Pole start,Pole goal, Pole temp) {// Make a stack just big enoughStack S = new AStack(2*n+1);S.push(new TOHobj(operation.TOH, n,start, goal, temp));while (S.length() > 0) {TOHobj it = S.pop(); // Get next taskif (it.op == operation.MOVE) // Do a movemove(it.start, it.goal);else if (it.num > 0) { // Imitate TOH recursive// solution (in reverse)S.push(new TOHobj(operation.TOH, it.num-1,it.temp, it.goal, it.start));S.push(new TOHobj(operation.MOVE, it.start,it.goal)); // A move to doS.push(new TOHobj(operation.TOH, it.num-1,it.start, it.temp, it.goal));}}}Figure 4.23 Stack-based implementation for Towers of Hanoi.move operation actually needs only to store information about two poles.Thus, there are two constructors: one to store the state when imitating arecursive call, and one to store the state for a move operation.An array-based stack is used because we know that the stack will needto store exactly 2n+1 elements. The new version of TOH begins by placingon the stack a description of the initial problem for n rings. The rest ofthe function is simply a while loop that pops the stack and executes theappropriate operation. In the case of a TOH operation (for n > 0), westore on the stack representations for the three operations executed by therecursive version. However, these operations must be placed on the stackin reverse order, so that they will be popped off in the correct order.