Tower of Hanoi is a mathematical puzzle where we have three rods and n disks. The objective of the puzzle is to move the entire stack to another rod, obeying the following simple rules:

1) Only one disk can be moved at a time.

2) Each move consists of taking the upper disk from one of the stacks and placing it on top of another stack i.e. a disk can only be moved if it is the uppermost disk on a stack.

3) No disk may be placed on top of a smaller disk.

Approach :

Take an example for 2 disks : Let rod 1 = 'A', rod 2 = 'B', rod 3 = 'C'. Step 1 : Shift first disk from 'A' to 'B'. Step 2 : Shift second disk from 'A' to 'C'. Step 3 : Shift first disk from 'B' to 'C'. The pattern here is : Shift 'n-1' disks from 'A' to 'B'. Shift last disk from 'A' to 'C'. Shift 'n-1' disks from 'B' to 'C'. Image illustration for 3 disks : Image Source : http://mathforum.org/dr.math/faq/faq.disk3.gif

Examples:

Input : 2 Output : Disk 1 moved from A to B Disk 2 moved from A to C Disk 1 moved from B to C Input : 3 Output : Disk 1 moved from A to C Disk 2 moved from A to B Disk 1 moved from C to B Disk 3 moved from A to C Disk 1 moved from B to A Disk 2 moved from B to C Disk 1 moved from A to C

#include <stdio.h> // C recursive function to solve tower of hanoi puzzle void towerOfHanoi(int n, char from_rod, char to_rod, char aux_rod) { if (n == 1) { printf("\n Move disk 1 from rod %c to rod %c", from_rod, to_rod); return; } towerOfHanoi(n-1, from_rod, aux_rod, to_rod); printf("\n Move disk %d from rod %c to rod %c", n, from_rod, to_rod); towerOfHanoi(n-1, aux_rod, to_rod, from_rod); } int main() { int n = 4; // Number of disks towerOfHanoi(n, 'A', 'C', 'B'); // A, B and C are names of rods return 0; }

Output:

Move disk 1 from rod A to rod B Move disk 2 from rod A to rod C Move disk 1 from rod B to rod C Move disk 3 from rod A to rod B Move disk 1 from rod C to rod A Move disk 2 from rod C to rod B Move disk 1 from rod A to rod B Move disk 4 from rod A to rod C Move disk 1 from rod B to rod C Move disk 2 from rod B to rod A Move disk 1 from rod C to rod A Move disk 3 from rod B to rod C Move disk 1 from rod A to rod B Move disk 2 from rod A to rod C Move disk 1 from rod B to rod C

For n disks, total 2^{n} – 1 moves are required.

**Related Articles**

**References:**

http://en.wikipedia.org/wiki/Tower_of_Hanoi

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