Self-describing numbers: Difference between revisions

{{confusing|c}}

{{improve|c|This implementation is hard to read and understand. It's in need of deobfuscation.}}

<lang c>#include <stdio.h>

int self_desc(const char *s)

{

unsigned char cnt[10] = {0};

int i;

for (i = 0; s[i] != '\0'; i++) cnt[s[i] - '0']++;

for (i = 0; s[i] != '\0'; i++) if (cnt[i] + '0' != s[i]) return 0;

return 1;

}

void gen(int n)

{

char d[11];

int one, i;

/* one = 0 may be confusing. 'one' is the number of digit 1s */

for (one = 0; one <= 2 && one < n - 2; one++) {

for (i = 0; i <= n; d[i++] = 0);

if ((d[0] = n - 2 - one) != 2) {

d[2] = d[d[0] - 0] = 1;

d[1] = 2;

} else {

d[1] = one ? 1 : 0;

d[2] = 2;

}

for (i = 0; i < n; d[i++] += '0');

if (self_desc(d)) printf("%s\n", d);

}

}

int main()

{

int i;

const char *nums[] = { "1210", "1337", "2020", "21200", "3211000", "42101000", 0};

for (i = 0; nums[i]; i++)

printf("%s is %sself describing\n", nums[i],

self_desc(nums[i]) ? "" : "not ");

printf("\nAll autobiograph numbers:\n");

for (i = 0; i < 11; i++) gen(i);

return 0;

}</lang>output<lang>1210 is self describing

1337 is not self describing

2020 is self describing

21200 is self describing

3211000 is self describing

42101000 is self describing

All autobiograph numbers:

2020

1210

21200

3211000

42101000

521001000

6210001000</lang>

===Alternative version===