Unique Paths with Obstacles

let uniquePathsWithObstacles = function(obstacleGrid) {

    if (!obstacleGrid || !obstacleGrid.length) return 0;

    function markNextRowsAsZero(col) {
        for (let i = col; i < maxCol; i++) {
            obstacleGrid[0][i] = 0;
        }
    }
    function markNextColumnsAsZero(row) {
        for (let i = row; i < maxRow; i++) {
            obstacleGrid[i][0] = 0;
        }
    }

    let maxRow = obstacleGrid.length,
        maxCol = obstacleGrid[0].length,
        OBSTACLE = 1, VISITED = -1;

    // first block is obstacle return 0;
    if (obstacleGrid[0][0] === OBSTACLE) {
        return 0;
    }

    // mark all first rows as either 1 or zero
    for (let col = 0; col < maxCol;col++) {
        if (obstacleGrid[0][col] === OBSTACLE) {
            markNextRowsAsZero(col);
            break;
        }
        else {
            obstacleGrid[0][col] = 1;
        }
    }

    // mark all first columns as either 1 or zero
    for (let row = 1; row < maxRow;row++) {
        if (obstacleGrid[row][0] === OBSTACLE) {
            markNextColumnsAsZero(row);
            break;
        }
        else {
            obstacleGrid[row][0] = 1;
        }
    }

    for (let row = 1; row < maxRow;row++) {
        for (let col = 1; col < maxCol;col++) {
            if (obstacleGrid[row][col] === OBSTACLE) {
                obstacleGrid[row][col] = 0;
            }
            else {
                obstacleGrid[row][col] =
                    obstacleGrid[row - 1][col] +
                    obstacleGrid[row][col - 1];
            }

        }
    }

    return obstacleGrid[maxRow - 1][maxCol - 1];
};