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@@ -0,0 +1,27 @@
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+#include <cstdio>
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+#include <cstring>
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+
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+using namespace std;
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+
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+const int N = 20;
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+
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+bool flag[N + 1][2 * N + 1];
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+
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+int dfs(int x, int y, int n) {
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+ if (n == 0) return 1;
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+ int cnt = 0;
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+ flag[x][y] = true;
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+ if (!flag[x + 1][y]) cnt += dfs(x + 1, y, n - 1);
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+ if (!flag[x][y + 1]) cnt += dfs(x, y + 1, n - 1);
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+ if (!flag[x][y - 1]) cnt += dfs(x, y - 1, n - 1);
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+ flag[x][y] = false;
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+ return cnt;
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+}
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+
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+int main() {
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+ int n;
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+ scanf("%d", &n);
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+ memset(flag, 0, sizeof(flag));
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+ printf("%d\n", dfs(0, N, n));
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+ return 0;
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+}
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