111 lines
2 KiB
C
111 lines
2 KiB
C
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#include "rbassert.h"
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#include <string.h>
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#include "puzzles.h"
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/* horrific and doesn't check overflow. */
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static long factx(long x, long y)
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{
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long acc = 1, i;
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for (i = y; i <= x; i++)
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acc *= i;
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return acc;
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}
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void reset_combi(combi_ctx *combi)
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{
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int i;
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combi->nleft = combi->total;
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for (i = 0; i < combi->r; i++)
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combi->a[i] = i;
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}
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combi_ctx *new_combi(int r, int n)
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{
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long nfr, nrf;
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combi_ctx *combi;
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assert(r <= n);
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assert(n >= 1);
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combi = snew(combi_ctx);
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memset(combi, 0, sizeof(combi_ctx));
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combi->r = r;
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combi->n = n;
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combi->a = snewn(r, int);
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memset(combi->a, 0, r * sizeof(int));
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nfr = factx(n, r+1);
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nrf = factx(n-r, 1);
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combi->total = (int)(nfr / nrf);
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reset_combi(combi);
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return combi;
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}
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/* returns NULL when we're done otherwise returns input. */
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combi_ctx *next_combi(combi_ctx *combi)
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{
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int i = combi->r - 1, j;
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if (combi->nleft == combi->total)
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goto done;
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else if (combi->nleft <= 0)
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return NULL;
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while (combi->a[i] == combi->n - combi->r + i)
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i--;
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combi->a[i] += 1;
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for (j = i+1; j < combi->r; j++)
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combi->a[j] = combi->a[i] + j - i;
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done:
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combi->nleft--;
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return combi;
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}
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void free_combi(combi_ctx *combi)
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{
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sfree(combi->a);
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sfree(combi);
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}
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/* compile this with:
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* gcc -o combi.exe -DSTANDALONE_COMBI_TEST combi.c malloc.c
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*/
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#ifdef STANDALONE_COMBI_TEST
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#include <stdio.h>
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void fatal(char *fmt, ...)
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{
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abort();
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}
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int main(int argc, char *argv[])
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{
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combi_ctx *c;
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int i, r, n;
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if (argc < 3) {
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fprintf(stderr, "Usage: combi R N\n");
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exit(1);
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}
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r = atoi(argv[1]); n = atoi(argv[2]);
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c = new_combi(r, n);
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printf("combi %d of %d, %d elements.\n", c->r, c->n, c->total);
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while (next_combi(c)) {
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for (i = 0; i < c->r; i++) {
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printf("%d ", c->a[i]);
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}
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printf("\n");
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}
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free_combi(c);
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}
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#endif
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