message: Update n-th-tribonacci-number.cpp
diff: class Solution {
  public:
  int tribonacci(int n) {
  - vector<vector<int>> T = {{1, 1, 1},
  - {1, 0, 0},
  - {0, 1, 0}};
  - return matrixExpo(T, n)[1][0];
  + vector<vector<int>> T = {{1, 1, 0},
  + {1, 0, 1},
  + {1, 0, 0}};
  + return matrixMult({{1, 0, 0}}, matrixExpo(T, n))[0][1]; // [a1, a0, a(-1)] * T^n
  }
  private:
  @@ -28,7 +28,7 @@ private:
  }
  vector<vector<int>> matrixMult(const vector<vector<int>>& A, const vector<vector<int>>& B) {
  - vector<vector<int>> result(A.size(), vector<int>(A.size()));
  + vector<vector<int>> result(A.size(), vector<int>(B[0].size()));
  for (int i = 0; i < A.size(); ++i) {
  for (int j = 0; j < B[0].size(); ++j) {
  int64_t entry = 0;
  