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| 1 | +class Solution { |
| 2 | +public: |
| 3 | + int knightDialer(int n) { |
| 4 | + const int mod = 1e9 + 7; |
| 5 | + vector<vector<int>> base = { |
| 6 | + {0, 0, 0, 0, 1, 0, 1, 0, 0, 0}, |
| 7 | + {0, 0, 0, 0, 0, 0, 1, 0, 1, 0}, |
| 8 | + {0, 0, 0, 0, 0, 0, 0, 1, 0, 1}, |
| 9 | + {0, 0, 0, 0, 1, 0, 0, 0, 1, 0}, |
| 10 | + {1, 0, 0, 1, 0, 0, 0, 0, 0, 1}, |
| 11 | + {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, |
| 12 | + {1, 1, 0, 0, 0, 0, 0, 1, 0, 0}, |
| 13 | + {0, 0, 1, 0, 0, 0, 1, 0, 0, 0}, |
| 14 | + {0, 1, 0, 1, 0, 0, 0, 0, 0, 0}, |
| 15 | + {0, 0, 1, 0, 1, 0, 0, 0, 0, 0}}; |
| 16 | + vector<vector<int>> res = pow(base, n - 1, mod); |
| 17 | + return accumulate(res[0].begin(), res[0].end(), 0LL) % mod; |
| 18 | + } |
| 19 | + |
| 20 | +private: |
| 21 | + vector<vector<int>> mul(const vector<vector<int>>& a, const vector<vector<int>>& b, int mod) { |
| 22 | + int m = a.size(), n = b[0].size(); |
| 23 | + vector<vector<int>> c(m, vector<int>(n, 0)); |
| 24 | + for (int i = 0; i < m; ++i) { |
| 25 | + for (int j = 0; j < n; ++j) { |
| 26 | + for (int k = 0; k < b.size(); ++k) { |
| 27 | + c[i][j] = (c[i][j] + (1LL * a[i][k] * b[k][j]) % mod) % mod; |
| 28 | + } |
| 29 | + } |
| 30 | + } |
| 31 | + return c; |
| 32 | + } |
| 33 | + |
| 34 | + vector<vector<int>> pow(vector<vector<int>>& a, int n, int mod) { |
| 35 | + int size = a.size(); |
| 36 | + vector<vector<int>> res(1, vector<int>(size, 1)); |
| 37 | + while (n > 0) { |
| 38 | + if (n % 2 == 1) { |
| 39 | + res = mul(res, a, mod); |
| 40 | + } |
| 41 | + a = mul(a, a, mod); |
| 42 | + n /= 2; |
| 43 | + } |
| 44 | + return res; |
| 45 | + } |
| 46 | +}; |
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