#904 · #885 · Spiral Matrix III(螺旋矩阵 III)

Starting at (rStart, cStart) in a rows x cols grid, walk clockwise in a spiral: east, south, west, north, then east again, expanding the radius each time a full cycle is completed. Return the coordinates of all rows * cols cells in the order they are first visited, skipping any cell outside the grid. Constraints: 1 <= rows, cols <= 100, 0 <= rStart < rows, 0 <= cStart < cols.