class Solution {
  public int uniquePathsWithObstacles(int[][] grid) {
    int R = grid.length;
    int C = grid[0].length;

    if (R == 0 || C == 0) return 0;

    // if first column has obstacle, no path to destination
    if (grid[0][0] == 1) return 0;

    grid[0][0] = 1;

    // if cell in first row contains obstacle,
    // set 0 to that cell and all cell after.
    for (int col = 1; col < C; col++) {
      grid[0][col] = grid[0][col] == 1 ? 0 : grid[0][col - 1];
    }

    // if cell in first column contians obstacle,
    // set 0 to that cell and all cell after.
    for (int row = 1; row < R; row++) {
      grid[row][0] = grid[row][0] == 1 ? 0 : grid[row - 1][0];
    }

    for (int row = 1; row < R; row++) {
      for (int col = 1; col < C; col++) {
        if (grid[row][col] == 1) {
          // set 0 to cell is obstacle
          grid[row][col] = 0;
        } else {
          grid[row][col] = grid[row - 1][col] + grid[row][col - 1];
        }
      }
    }

    return grid[R - 1][C - 1];
  }
}