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Facebook Interview Question for SDE1s


Country: United States



Comment hidden because of low score. Click to expand.
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of 0 vote

function findPath($fld, $src, $dst, &$visited = array()) {
    // check if reached destination
    if ($src['x'] == $dst['x'] && $src['y'] == $dst['y']) return [['x' => $src['x'], 'y' => $src['y']]];

    // check if in the borders
    if ($src['x'] < 0 || $src['x'] >= count($fld[0])) return false;
    if ($src['y'] < 0 || $src['y'] >= count($fld)) return false;

    // check if not "0" cell
    if ($fld[$src['y']][$src['x']] == 0) return false;

    // check if visited
    $srcKey = "{$src['x']},{$src['y']}";
    if (isset($visited[$srcKey])) return false;

    // mark this cell as visited
    $visited[$srcKey] = true;

    // check children
    $minPath = [];
    $path = findPath($fld, ['x' => $src['x'] - 1, 'y' => $src['y']], $dst, $visited);
    if ($path !== false && (empty($minPath) || count($path) < count($minPath))) $minPath = $path;

    $path = findPath($fld, ['x' => $src['x'] + 1, 'y' => $src['y']], $dst, $visited);
    if ($path !== false && (empty($minPath) || count($path) < count($minPath))) $minPath = $path;

    $path = findPath($fld, ['x' => $src['x'], 'y' => $src['y'] + 1], $dst, $visited);
    if ($path !== false && (empty($minPath) || count($path) < count($minPath))) $minPath = $path;

    $path = findPath($fld, ['x' => $src['x'], 'y' => $src['y'] - 1], $dst, $visited);
    if ($path !== false && (empty($minPath) || count($path) < count($minPath))) $minPath = $path;

    if (!empty($minPath)) {
        $minPath[] = $src;
        return $minPath;
    } else {
        return false;
    }
}

- sgchris January 17, 2018 | Flag Reply
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of 0 vote

package Main;

public class MinPath {

public static void main(String[] args) {

int xStart = 4, yStart = 4;

int xEnd = 0, yEnd = 2;

int[][] map = {{0, 1, 1, 0, 0},
{0, 0, 1, 0, 0},
{0, 1, 1, 1, 1},
{1, 1, 0, 0, 1},
{1, 1, 1, 1, 1}};

int[][] visitMap = {{0,0,0,0,0},
{0,0,0,0,0},
{0,0,0,0,0},
{0,0,0,0,0},
{0,0,0,0,0}};

visitMap[xStart][yStart] = 1;

int length = new MinPath().path(map, visitMap, xStart, yStart, xEnd, yEnd);

System.out.println(length);

}

public int path(int[][] map, int[][] visitMap, int xStart, int yStart, int xEnd, int yEnd) {

visitMap[xStart][yStart] = 1;

//path does not exist
int length = 0;

if(xStart == xEnd && yStart == yEnd) {
return 1;
}

//move left
if(yStart - 1 > -1 && map[xStart][yStart - 1] == 1 && visitMap[xStart][yStart - 1] == 0){
int length1 = path(map, copy(visitMap), xStart, yStart-1, xEnd, yEnd);
if(length1 == 0) {
length = length > length1 ? length: length1;
}
else {
length1++;
if(length != 0) {
length = length > length1 ? length1 : length;
} else {
length = length1;
}
}
}

//move right
if(yStart + 1 < map[0].length && map[xStart][yStart + 1] == 1 && visitMap[xStart][yStart + 1] == 0){
int length2 = path(map, copy(visitMap), xStart, yStart + 1, xEnd, yEnd);
if(length2 == 0) {
length = length > length2 ? length: length2;
}
else {
length2++;
if(length != 0) {
length = length > length2 ? length2 : length;
} else {
length = length2;
}
}
}

//move upward
if(xStart - 1 > -1 && map[xStart-1][yStart] == 1 && visitMap[xStart-1][yStart] == 0){
int length3 = path(map, copy(visitMap), xStart-1, yStart, xEnd, yEnd);
if(length3 == 0) {
length = length > length3 ? length: length3;
}
else {
length3++;
if(length != 0) {
length = length > length3 ? length3 : length;
} else {
length = length3;
}
}
}


//move downward


return length;
}

public int[][] copy(int[][] original) {
int[][] c = new int[original.length][original[0].length];

for(int i=0; i<original.length; i++)
for(int j=0; j<original[0].length; j++)
c[i][j] = original[i][j];

return c;
}

}

- Vladimir February 06, 2018 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 vote

package Main;

public class MinPath {

	public static void main(String[] args) {
		
		int xStart = 4, yStart = 4;
		
		int xEnd = 0, yEnd = 2;
		
		int[][] map = {{0, 1, 1, 0, 0}, 
			   	   	   {0, 0, 1, 0, 0}, 
			   	   	   {0, 1, 1, 1, 1},
			   	   	   {1, 1, 0, 0, 1},
			   	   	   {1, 1, 1, 1, 1}};
		
		int[][] visitMap = {{0,0,0,0,0},
							{0,0,0,0,0},
							{0,0,0,0,0},
							{0,0,0,0,0},
							{0,0,0,0,0}};
		
		visitMap[xStart][yStart] = 1;
		
		int length = new MinPath().path(map, visitMap, xStart, yStart, xEnd, yEnd);
		
		System.out.println(length);
		
	}
	
	public int path(int[][] map, int[][] visitMap, int xStart, int yStart, int xEnd, int yEnd) {
		
		visitMap[xStart][yStart] = 1;
		
		//path does not exist
		int length = 0;
		
		if(xStart == xEnd && yStart == yEnd) {
			return 1;
		}
		
		//move left
		if(yStart - 1 > -1 && map[xStart][yStart - 1] == 1 && visitMap[xStart][yStart - 1] == 0){
			int length1 = path(map, copy(visitMap), xStart, yStart-1, xEnd, yEnd);
			if(length1 == 0) {
				length = length > length1 ? length: length1;
			}
			else { 
				length1++;
				if(length != 0) {
					length = length > length1 ? length1 : length;
				} else {
					length = length1;
				}	
			}
		}
		
		//move right
		if(yStart + 1 < map[0].length && map[xStart][yStart + 1] == 1 && visitMap[xStart][yStart + 1] == 0){
			int length2 = path(map, copy(visitMap), xStart, yStart + 1, xEnd, yEnd);
			if(length2 == 0) {
				length = length > length2 ? length: length2;
			}
			else { 
				length2++;
				if(length != 0) {
					length = length > length2 ? length2 : length;
				} else {
					length = length2;
				}
			}
		}
		
		//move upward
		if(xStart - 1 > -1 && map[xStart-1][yStart] == 1 && visitMap[xStart-1][yStart] == 0){
			int length3 = path(map, copy(visitMap), xStart-1, yStart, xEnd, yEnd);
			if(length3 == 0) {
				length = length > length3 ? length: length3;
			}
			else { 
				length3++;
				if(length != 0) {
					length = length > length3 ? length3 : length;
				} else {
					length = length3;
				}
			}
		}
		
		
		//move downward
		
		
		return length;
	}
	
	public int[][] copy(int[][] original) {
		int[][] c = new int[original.length][original[0].length];
		
		for(int i=0; i<original.length; i++)
			for(int j=0; j<original[0].length; j++)
				c[i][j] = original[i][j];
		
		return c;
	}
	
}

- Vladimir February 06, 2018 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 vote

public class dfs {
static int[][] map = {
{0, 1, 0},
{1, 1, 0,},
{1, 1, 1}};


static int shortP(int i, int j, int dx, int dy) {
if ( i >= map.length || j >= map.length || i < 0 || j < 0)
return 100000;
else if (map[i][j] == 0 )
return 100000;
else {
map[i][j] = 0;
if (i == dx && j == dy)
return 0;
return Math.min(
Math.min(shortP(i + 1, j, dx, dy) + 1, shortP(i, j + 1, dx, dy)) + 1,
Math.min(shortP(i - 1, j, dx, dy) + 1, shortP(i, j - 1, dx, dy) + 1));
}
}

public static void main(String[] arg) {
int l = shortP(1, 0, 2, 2);
System.out.println(l);

}
}

- Anonymous March 29, 2018 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 vote

public class dfs {
    static int[][] map = {
            {0, 1, 0},
            {1, 1, 0,},
            {1, 1, 1}};


    static int shortP(int i, int j, int dx, int dy) {
         if ( i >= map.length || j >= map.length || i < 0 || j < 0)
             return  100000;
         else if (map[i][j] == 0 )
             return  100000;
         else {
            map[i][j] = 0;
            if (i == dx && j == dy)
                return 0;
            return Math.min(
                    Math.min(shortP(i + 1, j, dx, dy) + 1, shortP(i, j + 1, dx, dy)) + 1,
                    Math.min(shortP(i - 1, j, dx, dy) + 1, shortP(i, j - 1, dx, dy) + 1));
        }
    }

    public static void main(String[] arg) {
        int l = shortP(1, 0, 2, 2);
        System.out.println(l);

    }
}

- Anonymous March 29, 2018 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 vote

public class dfs {
    static int[][] map = {
            {0, 1, 0},
            {1, 1, 0,},
            {1, 1, 1}};


    static int shortP(int i, int j, int dx, int dy) {
         if ( i >= map.length || j >= map.length || i < 0 || j < 0)
             return  100000;
         else if (map[i][j] == 0 )
             return  100000;
         else {
            map[i][j] = 0;
            if (i == dx && j == dy)
                return 0;
            return Math.min(
                    Math.min(shortP(i + 1, j, dx, dy) + 1, shortP(i, j + 1, dx, dy)) + 1,
                    Math.min(shortP(i - 1, j, dx, dy) + 1, shortP(i, j - 1, dx, dy) + 1));
        }
    }

    public static void main(String[] arg) {
        int l = shortP(1, 0, 2, 2);
        System.out.println(l);

    }
}

- shachar March 29, 2018 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 vote

import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;
	
public class PathFinderUseDFS {
	class Cell {
		short x,y;
		
		public Cell(short x, short y){
			this.x = x;
			this.y = y;
		}
		
		@Override
	    public boolean equals(Object o) { 
	        if (o == this) { 
	            return true; 
	        } 
	  
	        if (!(o instanceof Cell)) { 
	            return false; 
	        } 
	          
	        Cell c = (Cell) o; 
	        return (x == c.x) && (y == c.y); 
	    }
		
		@Override
	    public int hashCode() {
	        return (new Short(x)).hashCode() + (new Short(y)).hashCode();
	    }

	}
	
	public static void main(String[] args){
		short[][] testcase = {
				{1,1,0,1},
				{0,1,1,1},
				{0,1,0,1},
				{1,1,1,1}
		};
		
		// for DFS using recursive function leads to cleaner code 
		// vs handling the recursion stack during the interview
		PathFinderUseDFS evaluator = new PathFinderUseDFS(testcase);
		
		evaluator.findAndPrintShortestPath((short) 0, (short) 0, (short) 0, (short) 3);
	}
	
	short[][] grid;
	int n,m;
	List<Cell> shortestPath;
	
	public PathFinderUseDFS(short[][] grid){
		this.grid = grid;
		n = grid.length;
		m = grid.length;
	}
	
	public void findAndPrintShortestPath(
			short startX, short startY,
			short endX, short endY) {
		// check start, end in grid
		// check if start and end are valid cells
		
		int maxDistance = n*m;
		int distance[][] = new int[n][m];
		for (int i = 0; i < n; i++){
			for (int j = 0; j < m; j++) {
				distance[i][j] = maxDistance;
			}
		}
		
		List<Cell> currentPath = new LinkedList<Cell>();
		Set<Cell> nodesInCurrentPath = new HashSet<Cell>();
		Cell start = new Cell(startX, startY);
		currentPath.add(start);
		nodesInCurrentPath.add(start);
		
		shortestPath = new LinkedList<Cell>();
		findShortestPath(endX, endY,
				start, currentPath, nodesInCurrentPath, distance);
				
		// print shortest path
		System.out.print("shortest path ");
		for (Cell cell : shortestPath) {
			System.out.print("(" + cell.x + "," + cell.y + ") ");
		}
		System.out.println();
	}
	
	public void findShortestPath(
			short endX, short endY,
			Cell cell, List<Cell> currentPath, Set<Cell> nodesInCurrentPath, 
			int[][] distance) {
		// base cases
		if (grid[cell.x][cell.y] == 0) {
			return;
		}
		
		// check distance 
		// if smaller add neighbors
		int currentPathLength = currentPath.size() - 1;
		if (currentPathLength < distance[cell.x][cell.y]){
			distance[cell.x][cell.y] = currentPathLength;
			// base case
			if ((cell.x == endX) && (cell.y == endY)) {
				// update overall shortest path
				shortestPath = new LinkedList<Cell>(currentPath);
				return ;
			}
			
			List<Cell> neighbors = new LinkedList<Cell>();
			if (cell.x - 1 >= 0) {
				neighbors.add(new Cell((short)(cell.x-1), cell.y));
			}
			if (cell.x + 1 < n) {
				neighbors.add(new Cell((short)(cell.x+1), cell.y));
			}
			if (cell.y - 1 >= 0) {
				neighbors.add(new Cell(cell.x, (short)(cell.y-1)));
			}
			if (cell.y + 1 < m) {
				neighbors.add(new Cell(cell.x, (short)(cell.y+1)));
			}
			
			for (Cell neighbor : neighbors) {
				if (!nodesInCurrentPath.contains(neighbor)){
					// update current path
					currentPath.add(neighbor);
					nodesInCurrentPath.add(neighbor);
					
					findShortestPath(endX, endY,
							neighbor, currentPath, nodesInCurrentPath, distance);
					
					// undo changes to current path
					currentPath.remove(neighbor);
					nodesInCurrentPath.remove(neighbor);
				}
			}
		}
		
	}
}

- just_do_it November 14, 2018 | Flag Reply


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