uva 129 回溯

#include <bits/stdc++.h>using namespace std;int n, k, cnt, S[100000], L;int dfs(int cur){if (cnt++ == n){for (int i = 0; i < cur; i++){cout << char('A' + S[i]);if ((i + 1) % 64 == 0 && i != cur - 1) cout << endl;else if ((i + 1) % 4 == 0 && i != cur - 1) cout << " ";}cout << endl;cout << cur << endl;return 0;}else for (int i = 0; i < L; i++){S[cur] = i;int ok = 1;for (int j = 1; j * 2 <= cur + 1; j++){bool equal = 1;for (int k = 0; k < j; k++)if (S[cur - k] != S[cur - k - j]){equal = 0; break;}if (equal) {ok = 0; break;}}if (ok) if (!dfs(cur + 1)) return 0;}return 1;}int main(int argc, char const *argv[]){while (cin >> n >> L){if (n == 0 && L == 0) break;cnt = 0;memset(S, 0, sizeof(S));dfs(0);}return 0;}