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Ackermann function computed with stack simulation
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/* | |
* Copyright (c) 2020 by Reto Kromer | |
* | |
* Ackermann function: | |
* | |
* A(0,n) = n+1 | |
* A(m,0) = A(m-1,1) if m > 0 | |
* A(m,n) = A(m-1,A(m,n-1)) if m > 0 and n > 0 | |
* | |
* where m and n are non-negative integers | |
* | |
* computed with stack simulation. | |
* | |
* This C program is released under a 3-Clause BSD License and is provided | |
* "as is" without warranty or support of any kind. | |
*/ | |
#include <stdio.h> | |
#include <stdlib.h> | |
int A(unsigned int m, unsigned int n) { | |
unsigned int s = 0, *M; | |
M = (unsigned int *)malloc(sizeof(unsigned int)); | |
if (M == NULL) { | |
fprintf(stderr, "Error: malloc failed.\n"); | |
exit(1); | |
} | |
for (;;) { | |
if (m == 0) { | |
if (s == 0) { | |
return ++n; | |
} else { | |
n++; | |
m = M[s--] - 1; | |
} | |
} else if (n == 0) { | |
m--; | |
n = 1; | |
} else { | |
M[++s] = m; | |
n--; | |
} | |
} | |
free(M); | |
return n; | |
} | |
int main(int argc, char* argv[]) { | |
unsigned int m, n; | |
if (argc == 3) { | |
m = atoi(argv[1]); | |
n = atoi(argv[2]); | |
} else { | |
printf("%s", "m = "); | |
scanf("%d", &m); | |
printf("%s", "n = "); | |
scanf("%d", &n); | |
} | |
printf("A(%d,%d) = %d\n", m, n, A(m,n)); | |
return 0; | |
} |
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