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/*
Challenge 017
Task #1
Create a script to demonstrate Ackermann function. The Ackermann function is
defined as below, m and n are positive number:
A(m, n) = n + 1 if m = 0
A(m, n) = A(m - 1, 1) if m > 0 and n = 0
A(m, n) = A(m - 1, A(m, n - 1)) if m > 0 and n > 0
Example expansions as shown in wiki page.
A(1, 2) = A(0, A(1, 1))
= A(0, A(0, A(1, 0)))
= A(0, A(0, A(0, 1)))
= A(0, A(0, 2))
= A(0, 3)
= 4
*/
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
int A(int m, int n) {
if (m==0)
return n+1;
else if (m>0 && n==0)
return A(m-1,1);
else if (m>0 && n>0)
return A(m-1, A(m, n-1));
else {
assert(0);
return 0;
}
}
int main(int argc, char* argv[]) {
if (argc != 3) {
fputs("usage: ch-1 m n", stderr);
return EXIT_FAILURE;
}
printf("%d\n", A(atoi(argv[1]), atoi(argv[2])));
}
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