obstacleGrid2.js

/**
 * @param {number[][]} obstacleGrid
 * @return {number}
 */
var uniquePathsWithObstacles = function(obstacleGrid) {
    
    const memo = new Array(obstacleGrid.length)
        .fill(0)
        .map(() => new Array(obstacleGrid[0].length).fill(null));
    
    const traverse = (i, j) => {
        
        if(i === obstacleGrid.length) return 0;
        if(j === obstacleGrid[0].length) return 0;
        if(obstacleGrid[i][j] === 1) return 0;
        
        if(i === obstacleGrid.length-1 && j === obstacleGrid[0].length-1){
            return 1;
        }
        
        if(memo[i][j] !== null) return memo[i][j];
        
        return memo[i][j] = traverse(i+1, j) + traverse(i, j+1);
    };
    
    return traverse(0, 0);
};