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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])));
+}