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Facebook Interview Question for Software Developers


Country: United States



Comment hidden because of low score. Click to expand.
1
of 3 vote

Using java, this code should work,

int max = -1;
for (ArrayList<Integer> i : mulList)
    max = (max < i.size()) ? i.size() : max;
tmp = new ArrayList<>();
for (int j = 0; j < max; j++)
    for (ArrayList<Integer> i : mulList)
        try {
            tmp.add(i.get(j));
        }
        catch (IndexOutOfBoundsException e) {}
System.out.println(tmp.toString());

- PeyarTheriyaa April 19, 2018 | Flag Reply
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0
of 0 votes

Such a poor style of code..

- Raaj July 13, 2019 | Flag
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0
of 0 votes

instead do like this

private static List<Integer> interleavedListSimple(List<List<Integer>> lists) {

        List<Integer> interleaveList = new ArrayList<>();

        int maxSize = 0;

        for (List<Integer> list : lists)
            maxSize = Math.max(maxSize, list.size());

        int index = 0;
        while (index < maxSize) {
            for (int i = 0; i < lists.size(); i++) {
                if (index < lists.get(i).size()) {
                    interleaveList.add(lists.get(i).get(index));
                }
            }
            index++;
        }


        return interleaveList;
    }

- nitinguptaiit July 13, 2019 | Flag
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0
of 0 vote

Solution in Scala using transpose:

object InterleaveArrays {
  def main(args: Array[String]): Unit = {
    val list1 = List(1,2,3)
    val list2 = List(9,0)
    val list3 = List(5)
    val list4 = List(-4, -5, -2, -3, -1)

    println(getInterleaved(list1, list2, list3, list4))
  }

  def transpose[A](xs: List[List[A]]): List[List[A]] = xs.filter(_.nonEmpty) match {
    case Nil    =>  Nil
    case ys: List[List[A]] => ys.map{ _.head }::transpose(ys.map{ _.tail })
  }

  def getInterleaved(lists : List[Int]*) : List[Int] = {
    transpose(lists.toList).flatten
  }
}

// prints List(1, 9, 5, -4, 2, 0, -5, 3, -2, -3, -1)

- guilhebl April 18, 2018 | Flag Reply
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0
of 0 vote

$input = [[1,2,3], [9, 0], [5], [-4,-5,-2,-3,-1]]; 

$maxlength = 0;
$output = array();

foreach($input as $list){
    if(count($list) > $maxlength){
        $maxlength = count($list);
    }
}

for($i = 0; $i < $maxlength; $i++){
     for($k = 0; $k < count($input); $k++){
         if(isset($input[$k][$i])){
             $output[] = $input[$k][$i];
         }
     }
}

print_r($output);

- Kris April 19, 2018 | Flag Reply
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0
of 0 vote

<?php

$input = [[1,2,3], [9, 0], [5], [-4,-5,-2,-3,-1]]; 

$maxlength = 0;
$output = array();

foreach($input as $list){
    if(count($list) > $maxlength){
        $maxlength = count($list);
    }
}

for($i = 0; $i < $maxlength; $i++){
     for($k = 0; $k < count($input); $k++){
         if(isset($input[$k][$i])){
             $output[] = $input[$k][$i];
         }
     }
}

print_r($output);

- Kris April 19, 2018 | Flag Reply
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0
of 0 vote

private List<Integer> interleaved( List<List<Integer>> listOfLists ) {
        List<Integer> list = new ArrayList<>();
        int size = listOfLists.size();
        int max = listOfLists.stream().mapToInt( s -> s.size() ).max().getAsInt();

        for ( int j = 0; j < max; j++ ) {
            for ( int i = 0; i < size; i++ ) {
                if (listOfLists.get( i ).size() > j) {
                    list.add( listOfLists.get( i ).get( j ) );
                }
            }
        }
        return list;
    }

- alltej April 20, 2018 | Flag Reply
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0
of 0 vote

private List<Integer> interleaved( List<List<Integer>> listOfLists ) {
        List<Integer> list = new ArrayList<>();
        int size = listOfLists.size();
        int max = listOfLists.stream().mapToInt( s -> s.size() ).max().getAsInt();

        for ( int j = 0; j < max; j++ ) {
            for ( int i = 0; i < size; i++ ) {
                if (listOfLists.get( i ).size() > j) {
                    list.add( listOfLists.get( i ).get( j ) );
                }
            }
        }
        return list;
    }

- alltej April 20, 2018 | Flag Reply
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0
of 0 vote

vector<int> interleave(const vector<vector<int>>& input) {
    vector<int> result;
    int index = 0;
    int maxSize = INT_MIN;
    
    for (auto i : input) {
        maxSize = max(maxSize, (int)i.size());
    }
    
    while (index < maxSize) {
        for (int i = 0; i < input.size(); i++) {
            if (index >= input[i].size())
                continue;
            result.push_back(input[i][index]);
        }
        index++;
    }
    return result;
}

- sue April 22, 2018 | Flag Reply
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0
of 0 vote

private static int[] interleaveLists(List<List<Integer>> ll){
    	if(ll == null)
    			return null;
    	int listLength = 0;
    	int total = 0;
    	for(List<Integer> list : ll){
    		if(list == null)
    			continue;
    		listLength = Math.max(list.size(), listLength);
    		total += list.size();
    	}
    	int[] result = new int[total];
    	int index = 0;
    	for(int i = 0; i < listLength; ++i){
    		for(List<Integer> list : ll){
    			if(list == null)
    				continue;
    				if(i < list.size()){
    					result[index++] = list.get(i);
    				}
    		}
    	}
    	return result;
    }

- popeye May 04, 2018 | Flag Reply
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0
of 0 vote

private static int[] interleaveLists(List<List<Integer>> ll){
    	if(ll == null)
    			return null;
    	int listLength = 0;
    	int total = 0;
    	for(List<Integer> list : ll){
    		if(list == null)
    			continue;
    		listLength = Math.max(list.size(), listLength);
    		total += list.size();
    	}
    	int[] result = new int[total];
    	int index = 0;
    	for(int i = 0; i < listLength; ++i){
    		for(List<Integer> list : ll){
    			if(list == null)
    				continue;
    				if(i < list.size()){
    					result[index++] = list.get(i);
    				}
    		}
    	}
    	return result;
    }

- popeye May 04, 2018 | Flag Reply
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0
of 0 vote

//C++
void interleave(vector<vector<int>> grid)
{
	int m = grid.size();
	int n = 0;
	
	for (int i = 0; i < m; i++)
		n = max(n, grid[i].size());
	vector<int> result;
	result.reserve(m*n);
	for (int j = 0; j < n; j++)
		for (int i = 0; i < m; i++)
			if (j < grid[i].size())
				result.push_back(grid[i][j]);
	for (auto i:result)
		cout << i << " ";
}

- aman.bansal4u May 19, 2018 | Flag Reply
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0
of 0 vote

### python
def interleave(ll):
    out = []
    while all_sublists(ll):
        for l in ll:
            if l:
                out.append(l.pop(0))
    return out

def all_sublists(ll):
    for l in ll:
        if l:
            return True
    return False

- slack0 May 23, 2018 | Flag Reply
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0
of 0 vote

public static List<Integer> mergeIntervals(final int[][] input) {

    int max = 0;
    final List<Integer> temp = new ArrayList<>();

    for (final int[] array : input) {
      if (array.length > max) {
        max = array.length;
      }
    }

    for (int k = 0; k < max; k++) {
      for (int j = 0; j < input.length; j++) {
        if (k < input[j].length) {
          temp.add(input[j][k]);
        }
      }
    }
    return temp;
  }

- Anonymous May 28, 2018 | Flag Reply
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0
of 0 vote

// using java 
public static List<Integer> mergeIntervals(final int[][] input) {

    int max = 0;
    final List<Integer> temp = new ArrayList<>();

    for (final int[] array : input) {
      if (array.length > max) {
        max = array.length;
      }
    }

    for (int k = 0; k < max; k++) {
      for (int j = 0; j < input.length; j++) {
        if (k < input[j].length) {
          temp.add(input[j][k]);
        }
      }
    }
    return temp;
  }

- Abereham May 28, 2018 | Flag Reply
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0
of 0 vote

def interleave_lists(ar):
    result = []
    max_length = 0
    for i in ar:
        max_length = max(max_length,len(i))

    for _ in range(max_length):
        for i in ar:
            if len(i) > 0:
                result.append(i.pop(0))
    return result

- Anonymous May 30, 2018 | Flag Reply
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0
of 0 vote

I received this question in Feb 2018. I was told that there could be an undefined amount of arrays in the array so [1,[2,[3,4,5]],6,[7,8],9] was a possible input. Also that you didn't know the if the next element was a number so I wrote it in java as:

private ArrayList<Number> printList(ArrayList<Object> input){
	ArrayList<Number> output = new ArrayList();
	for(Object o: input){
		if(o instanceof Number)
			output.add(o);
		else if (o instance of ArrayList)
			output.addAll(printList(o));
	}
	return output;
}

- Stefan June 21, 2018 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 vote

Here is my solution

int[][] input = { { 1, 2, 3 }, { 0, 9 }, { 5 }, { 4, 6, 7, 8 } };
//	     expected out put is [1,0,5,4,2,9,7,3,7,8]
		// int[] output = new int[];
		ArrayList<Integer> output = new ArrayList();
		int j = 0;
		while (j < input.length) {
			for (int i = 0; i < input.length; i++) {
				int[] arrayAtindex = input[i];
				if (j < arrayAtindex.length) {
					output.add(arrayAtindex[j]);

				}
			}
			j++;
		}
		System.out.println("output===>" + output);

- Sravani Cheripalli July 27, 2018 | Flag Reply
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0
of 0 vote

private void getInterleaveList() {
		int[][] input = { { 1, 2, 3 }, { 0, 9 }, { 5 }, { 4, 6, 7, 8 } };
//	     expected out put is [1,0,5,4,2,9,7,3,7,8]
		// int[] output = new int[];
		ArrayList<Integer> output = new ArrayList();
		int j = 0;
		while (j < input.length) {
			for (int i = 0; i < input.length; i++) {
				int[] arrayAtindex = input[i];
				if (j < arrayAtindex.length) {
					output.add(arrayAtindex[j]);
				}
			}
			j++;
		}
		System.out.println("output===>" + output);
	}

- Sravani Cheripalli July 27, 2018 | Flag Reply
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0
of 0 vote

private void getInterleaveList() {
int[][] input = { { 1, 2, 3 }, { 0, 9 }, { 5 }, { 4, 6, 7, 8 } };
// expected out put is [1,0,5,4,2,9,7,3,7,8]
// int[] output = new int[];
ArrayList<Integer> output = new ArrayList();
int j = 0;
while (j < input.length) {
for (int i = 0; i < input.length; i++) {
int[] arrayAtindex = input[i];
if (j < arrayAtindex.length) {
output.add(arrayAtindex[j]);
}
}
j++;
}
System.out.println("output===>" + output);
}

- Sravani Cheripalli July 27, 2018 | Flag Reply
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0
of 0 vote

class Solution {
  public static void main(String[] args) {

    // test case
    int[][] input = {{1,2,3}, {9, 0}, {5}, {-4,-5,-2,-3,-1}};

    int[] out = new int[input[0].length + input[1].length + input[2].length + input[3].length];

    out = interleaveList(input);
    for (int i = 0; i < out.length; i++)
      System.out.print(out[i] + " ");
  }
  
  static public int[] interleaveList(int[][] in) {
    
    // get max_len to cover all rows
    int max_len = 0;
    int size_all = 0; // size for all elements
    for (int i = 0; i < in.length; i++) {
      if (in[i].length > max_len)
        max_len = in[i].length;
      size_all += in[i].length;
    }
    
    int[] out = new int[size_all];
    int k = 0;
    // interleave in the loop
    for (int i = 0; i < max_len; i++) {
      for (int j = 0; j < in.length; j++) {
        if (i < in[j].length) {
          out[k++] = in[j][i];
        }
      }
    }
    
    return out;
  }
}

- CJ September 18, 2018 | Flag Reply
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0
of 0 vote

x = [[1,2,3],[5,6],[5],[-3,-4,-5,-6,-7]]
ans=[]

for j in range(len(x)):
out=[]
for i in x:
if i:
out.append(i.pop(0))
print(out)
ans.extend(out)

print(ans)

- Adi_ November 06, 2018 | Flag Reply
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0
of 0 vote

x = [[1,2,3],[5,6],[5],[-3,-4,-5,-6,-7]]
ans=[]

for j in range(len(x)):
    out=[]
    for i in x:
        if i:
            out.append(i.pop(0))
    print(out)
    ans.extend(out)

print(ans)

- Adi_ November 06, 2018 | Flag Reply
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0
of 0 vote

public class InterleavedList {

    static class Helper {
        public int listIndex = 0;
        public int selfIndex = 0;

        public Helper(int listIndex) {
            this.listIndex = listIndex;
        }

        @Override
        public String toString() {
            return "{" +
                    "listIndex=" + listIndex +
                    ", selfIndex=" + selfIndex +
                    '}';
        }
    }

    public static void main(String args[]) {

        List<List<Integer>> input = new ArrayList<>();

        List<Integer> one = new ArrayList<>();
        one.add(1);
        one.add(2);
        one.add(3);

        List<Integer> two = new ArrayList<>();
        two.add(9);
        two.add(0);

        List<Integer> three = new ArrayList<>();
        three.add(5);


        List<Integer> four = new ArrayList<>();
        four.add(-4);
        four.add(-5);
        four.add(-2);
        four.add(-3);
        four.add(-1);

        input.add(one);
        input.add(two);
        input.add(three);
        input.add(four);


        System.out.println(interleavedList(input));

    }


    private static List<Helper> getIndexList(int totalLists) {
        List<Helper> helpers = new ArrayList<>(totalLists);

        for (int i = 0; i < totalLists; i++) {
            helpers.add(new Helper(i));
        }

        return helpers;
    }

    private static List<Integer> interleavedList(List<List<Integer>> input) {

        int totalLists = input.size();

        //We use this list to iterate over input
        List<Helper> helpers = getIndexList(totalLists);
        int x = totalLists;

        List<Integer> result = new ArrayList<>();

        //We remove all the helper once their corresponding list exhaust


        while (true) {
            ListIterator<Helper> listIterator = helpers.listIterator();
            while (listIterator.hasNext()) {

                Helper h = listIterator.next();

                //get the inner list by listIndex
                List<Integer> inner = input.get(h.listIndex);

                if (h.selfIndex < inner.size()) {
                    result.add(inner.get(h.selfIndex++));
                } else {
                    //If all element traversed, remove it for next iteration
                    listIterator.remove();
                }

            }

            if (helpers.isEmpty())
                break;

        }


        return result;

    }
}

- nitinguptaiit April 02, 2019 | Flag Reply
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0
of 0 votes

This is very easy to understand; and has performance boost if one of the list size is >>> then other

- nitinguptaiit April 02, 2019 | Flag
Comment hidden because of low score. Click to expand.
0
of 0 votes

Another version of easy code ;

private static List<Integer> interleavedListSimple(List<List<Integer>> lists) {

        List<Integer> interleaveList = new ArrayList<>();

        int maxSize = 0;

        for (List<Integer> list : lists)
            maxSize = Math.max(maxSize, list.size());

        int index = 0;
        while (index < maxSize) {
            for (int i = 0; i < lists.size(); i++) {
                if (index < lists.get(i).size()) {
                    interleaveList.add(lists.get(i).get(index));
                }
            }
            index++;
        }


        return interleaveList;
    }

- nitinguptaiit July 13, 2019 | Flag
Comment hidden because of low score. Click to expand.
0
of 0 vote

Nearly optimal:

def merge_list_of_list( list_of_lists ){
    iterators = list( list_of_lists ) as { $.o.iterator }
    final_merge_list = list( )
    added = true 
    while ( added ){
        added = false 
        for ( it : iterators ){
            added = it.hasNext 
            if ( added ){
                final_merge_list += it.next // done 
            }
        }
    }
    final_merge_list // return 
}

- NoOne April 17, 2019 | Flag Reply
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0
of 0 vote

List<Integer> interleave(List<List<Integer>> items){
     if(items==null) return null ;
     int size=items.size();
     if(size==1) return items.get(0);
     List<Integer> res = new ArrayList<>();
     int idx=0;
     boolean hasNext=true;
     while(hasNext) {
         hasNext=false;
         for(List<Integer> list: items) {
             if(idx <list.size() ) {
                 res.add(list.get(idx));
                 hasNext=true;
             }
         }
         idx++;
     }
     return res;
   }

- Nitu October 12, 2019 | Flag Reply
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-1
of 1 vote

and
public class InterleaveList {
    /**
     * Interleave list of lists in Java
     * Example:
     * input = [[1,2,3], [9, 0], [5], [-4,-5,-2,-3,-1,5,2,234,2,24,24,4]];
     * output = [1,9,5,-4,2,0,-5,3,-2,-3,-1]
     */

    private static int[] findInterleaveList(int[][] arr) {

        List<Integer> interleaveList = new ArrayList<>();

        boolean shouldVisit = true;

        int index = 0;
        while (shouldVisit) {
            for (int i = 0; i < arr.length; i++) {
                if (index < arr[i].length) {
                    interleaveList.add(arr[i][index]);
                    shouldVisit = true;
                } else {
                    shouldVisit = false;
                }
            }
            index++;
        }


        int[] list = new int[interleaveList.size()];
        int position = 0;
        for (Integer integer : interleaveList) {
            list[position] = integer;
            position++;
        }

        return list;
    }

    public static void main(String[] args) {
        int[][] arr = {{1, 2, 3}, {9, 0}, {5}, {-4, -5, -2, -3, -1,5,2,234,2,24,24,4}};

        int[] output = findInterleaveList(arr);
        for (Integer interleave : output) {
            System.out.print(interleave);
            System.out.print("\t");
        }

    }
}

- Ajay April 19, 2018 | Flag Reply
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0
of 0 votes

Code is wrong; this assume the last list is always greater then other list size;
try below input
[[1,2,3], [9,0],[5,9], [-4] ]

output you produce is
[1, 9, 5, -4, 2, 0, 9]
where as it should be
[1, 9, 5, -4, 2, 0, 9, 3]

- nitinguptaiit July 13, 2019 | Flag
Comment hidden because of low score. Click to expand.
0
of 0 votes

here is the correct code

private static List<Integer> interleavedListSimple(List<List<Integer>> lists) {

        List<Integer> interleaveList = new ArrayList<>();

        int maxSize = 0;

        for (List<Integer> list : lists)
            maxSize = Math.max(maxSize, list.size());

        int index = 0;
        while (index < maxSize) {
            for (int i = 0; i < lists.size(); i++) {
                if (index < lists.get(i).size()) {
                    interleaveList.add(lists.get(i).get(index));
                }
            }
            index++;
        }


        return interleaveList;
    }

- nitinguptaiit July 13, 2019 | Flag


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