54. 螺旋矩阵

class Solution {
public:
  vector<int> spiralOrder(vector<vector<int>>& matrix) {
    int Rows = matrix.size(), Cols = matrix.front().size();
    // This looks clumsy at the first place, but it's really easy to get if you
    // just draw the trail on paper.
    int R = Cols, B = Rows - 1, L = Cols - 1, T = Rows - 2;
    // This naughty -1 also comes from the counting method above.
    int X = -1, Y = 0;

    vector<int> Result;
    int Remaining = Rows * Cols;
    while (Remaining) {
      for (int i = 0; i < R; ++i) {
        Result.push_back(matrix[Y][++X]);
        if (!--Remaining) return Result;
      }
      R -= 2;
      for (int i = 0; i < B; ++i) {
        Result.push_back(matrix[++Y][X]);
        if (!--Remaining) return Result;
      }
      B -= 2;
      for (int i = 0; i < L; ++i) {
        Result.push_back(matrix[Y][--X]);
        if (!--Remaining) return Result;
      }
      L -= 2;
      for (int i = 0; i < T; ++i) {
        Result.push_back(matrix[--Y][X]);
        if (!--Remaining) return Result;
      }
      T -= 2;
    }
    return Result;
  }
};