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Diffstat (limited to 'other/nth_tribonacci_number.cpp')
-rw-r--r-- | other/nth_tribonacci_number.cpp | 61 |
1 files changed, 0 insertions, 61 deletions
diff --git a/other/nth_tribonacci_number.cpp b/other/nth_tribonacci_number.cpp deleted file mode 100644 index cabdb39..0000000 --- a/other/nth_tribonacci_number.cpp +++ /dev/null @@ -1,61 +0,0 @@ -// 1137. N-th Tribonacci Number -#include "leetcode.h" - -/* - * the tribonacci sequence t^n is defined as follows - * t0 = 0, t1 = 1, t2 = 1, & tn+3 = tn + tn+1 + tn+2 for n >= 0 - * given n, return value of tn - * eg. - * n = 4, output: 4 - * t3 = 0 + 1 + 1 = 2 - * t4 = 1 + 1 + 2 = 4 - */ - -typedef long long ll; -struct Matrix { - vvd(ll) a; - int rows, cols; - Matrix(int rows = 0, int cols = 0) : rows(rows), cols(cols) { - a.resize(rows); - for (int i = 0; i < rows; ++i) - a[i].assign(cols, 0); - } - Matrix(const vvd(ll) & matrix) - : a(matrix), rows(matrix.size()), cols(matrix[0].size()) {} -}; - -Matrix operator*(const Matrix &a, const Matrix &b) { - Matrix res(a.rows, b.cols); - for (int i = 0; i < a.rows; ++i) - for (int j = 0; j < b.cols; ++j) - for (int k = 0; k < a.cols; ++k) - res.a[i][j] += a.a[i][k] * b.a[k][j]; - return res; -} - -Matrix fastPow(const Matrix &matrix, int pow) { - if (pow == 1) - return matrix; - Matrix half = fastPow(matrix, pow / 2); - if (pow & 1) - return half * half * matrix; - return half * half; -} - -class Solution { -public: - int tribonacci(int n) { - if (n == 0) - return 0; - Matrix m({{0, 1, 0}, {0, 0, 1}, {1, 1, 1}}); - Matrix m0({{0}, {1}, {1}}); - Matrix mn = fastPow(m, n) * m0; - return mn.a[0][0]; - } -}; - -int main() { - Solution obj; - cout << obj.tribonacci(4) << endl; // expect: 4 - cout << obj.tribonacci(25) << endl; // expect: 1389537 -} |