Facebook Interview Question for Android Engineers


Country: United States
Interview Type: Phone Interview




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void Combs(unordered_map<char, vector<char>> &map, string const &digits,
	vector<string> &combs, string const comb = "")
{
	if (comb.size() == digits.size()) {
		if (!comb.empty()) {
			combs.push_back(comb);
		}
		return;
	}
	auto it = map.find(digits[comb.size()]);
	if (it != map.end()) {
		vector<char> const &chars = it->second;
		for (char c : chars) {
			Combs(map, digits, combs, comb + c);	
		}
	}
}

- Alex November 09, 2017 | Flag Reply
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import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class CombLetters {

	static Map<String, String[]> map = new HashMap<String, String[]>();
	
	List<String> mix(String in, Map<String, String[]> map) {
		List<String[]> l = new ArrayList<String[]>();
		for (int i = 0; i < in.length(); i++) {
			l.add(map.get(in.substring(i, i + 1)));
		}
		List<String> res = new ArrayList<>();
		recMix(l, 0, "", res);
		return res;
	}
	void recMix(List<String[]> letsGr, int i, String s, List<String> res) {
		if (i == letsGr.size()) {
			res.add(s);
			return;
		}
		String[] lets = letsGr.get(i);
		for (int j = 0; j < lets.length; j++) {
			recMix(letsGr, i + 1, s + lets[j], res);
		}
	}
	
	public CombLetters() {
		map.put("1", new String[]{"a", "b", "c"});
		map.put("2", new String[]{"c", "d", "e"});
		map.put("3", new String[]{"f", "g", "h"});
	}
	public static void main(String[] args) {
		// TODO Auto-generated method stub

		List<String> l = new CombLetters().mix("12", map);
		System.out.println(l);//[ac, ad, ae, bc, bd, be, cc, cd, ce]
	}

}

- cemaivaz November 09, 2017 | Flag Reply
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JavaScript solution.

function helper(input, map, i, solution, solutions){
  if (i === input.length){
    solutions.push(solution);
    return;
  }

  const digit = input.charAt(i);
  const chars = map.get(digit);

  chars.forEach((c) => helper(input, map, i + 1, solution + c, solutions));
}

function mix(input, map){
  const solutions = [];
  helper(input, map, 0, '', solutions);
  return solutions;
}

const input = '12';
const map = new Map();
map.set('1', ['a', 'b', 'c']);
map.set('2', ['c', 'd', 'e']);
map.set('3', ['f', 'g', 'h']);

console.log(mix(input, map));

- Anonymous November 10, 2017 | Flag Reply
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Python Solution:

def crossword(dt,nums):
    # populate temp dict for the given numbers
    d = dict()
    for i in range(len(nums)):
        d[i] = dt.get(int(nums[i]))
    print(d)
    #call helper method with initial values
    helper(d,'',0)

#helper method implementation    
def helper(d,s,n):
    temp =[]
    if n == len(d):
        print(s)
    else:
        temp = d.get(n)
        for j in range(len(temp)):
            helper(d,s+temp[j],n+1)


dt = {1: ['a','b','c'], 2: ['d','e','f'],3:['g','h','i']}
crossword(dt,'31')
#Output
# ga gb gc ha hb hc ia ib ic

- praveenp November 10, 2017 | Flag Reply
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static void Main(string[] args)
{
    Dictionary<string, string[]> dict = new Dictionary<string, string[]>();
    dict.Add("1", new []{"a","b","c"});
    dict.Add("2", new [] { "d", "e","f"});
    dict.Add("3", new [] {"g", "h","i"});

    string input = "123";//Console.ReadLine();
    List<string> results = Mix(input, dict);
    Console.WriteLine($"Input: {input}, Output:");
    foreach(var s in results)
    {
        Console.WriteLine(s);
    }
}

static List<string> Mix(string input, Dictionary<string, string[]> dict)
{
    string key = null;
    List<string> results = new List<string>();
    List<string> tempResults = null;
    string[] keyChars = null;
    for(int i = 0; i<input.Length; i++)
    {
        key = input.Substring(i, 1);
        if(!dict.ContainsKey(key)) continue;

        keyChars = dict[key];
        if(i == 0)
        {
            results.AddRange(keyChars);
            continue;
        }

        tempResults = new List<string>(results);
        results = new List<string>();
        foreach(var s in tempResults)
        {
            foreach(var ss in keyChars)
            {
                results.Add(s+ss);
            }
        }
    }

    return results;
}

- Dave November 10, 2017 | Flag Reply
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static void Main(string[] args)
{
    Dictionary<string, string[]> dict = new Dictionary<string, string[]>();
    dict.Add("1", new []{"a","b","c"});
    dict.Add("2", new [] { "d", "e","f"});
    dict.Add("3", new [] {"g", "h","i"});

    string input = "123";//Console.ReadLine();
    List<string> results = Mix(input, dict);
    Console.WriteLine($"Input: {input}, Output:");
    foreach(var s in results)
    {
        Console.WriteLine(s);
    }
}

static List<string> Mix(string input, Dictionary<string, string[]> dict)
{
    string key = null;
    List<string> results = new List<string>();
    List<string> tempResults = null;
    string[] keyChars = null;
    for(int i = 0; i<input.Length; i++)
    {
        key = input.Substring(i, 1);
        if(!dict.ContainsKey(key)) continue;

        keyChars = dict[key];
        if(i == 0)
        {
            results.AddRange(keyChars);
            continue;
        }

        tempResults = new List<string>(results);
        results = new List<string>();
        foreach(var s in tempResults)
        {
            foreach(var ss in keyChars)
            {
                results.Add(s+ss);
            }
        }
    }

    return results;
}

- Dave November 10, 2017 | Flag Reply
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0
of 0 vote

static void Main(string[] args)
{
Dictionary<string, string[]> dict = new Dictionary<string, string[]>();
dict.Add("1", new []{"a","b","c"});
dict.Add("2", new [] { "d", "e","f"});
dict.Add("3", new [] {"g", "h","i"});

string input = "123";//Console.ReadLine();
List<string> results = Mix(input, dict);
Console.WriteLine($"Input: {input}, Output:");
foreach(var s in results)
{
Console.WriteLine(s);
}
}

static List<string> Mix(string input, Dictionary<string, string[]> dict)
{
string key = null;
List<string> results = new List<string>();
List<string> tempResults = null;
string[] keyChars = null;
for(int i = 0; i<input.Length; i++)
{
key = input.Substring(i, 1);
if(!dict.ContainsKey(key)) continue;

keyChars = dict[key];
if(i == 0)
{
results.AddRange(keyChars);
continue;
}

tempResults = new List<string>(results);
results = new List<string>();
foreach(var s in tempResults)
{
foreach(var ss in keyChars)
{
results.Add(s+ss);
}
}
}

return results;
}

- dave November 10, 2017 | Flag Reply
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Java solution

private static List<String> mix(String in, Map<String,String[]> map){
		List<String> returnList = null;
		for (int i = 0; i < in.length(); i++) {
			//get the current i 
			returnList = mix(returnList,Arrays.asList(map.get(""+in.charAt(i))));
		}
		return returnList;
	}
	private static List<String> mix(List<String> list1, List<String> list2){
		if(list1 == null) return list2;
		if(list2 == null) return list1;		
		List<String> returnList = new ArrayList<>(list1.size()*list2.size());
		for(String str1:list1)
			for(String str2:list2)
				returnList.add(str1+str2);
		return returnList;
	}

- naren November 12, 2017 | Flag Reply
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of 0 vote

import java.util.List;
import java.util.Vector;
import java.util.Map;
import java.util.HashMap;

public class Mixer {

 public static List<String> mix(String in, Map<String, String[]> map) {
        List<String> combs = new Vector<String>();
        int indexes[] = new int[in.length()];

        do {
                String word="";
                for(int i=0;i<in.length();i++) word += map.get(Character.toString(in.charAt(i)))[indexes[i]];
                combs.add(word);
        } while(increment(indexes,0) == 0);

        return combs;
}

 private static int increment(int[] indexes, int order) {
        if(order == indexes.length -1 && indexes[order]==2) return -1;
        if(++indexes[order] == 3)
        {
           indexes[order]=0;
           return increment(indexes, ++order);
        }
        return 0;
}

 public static void main(String args[]) {
        Map<String, String[]> map = new HashMap<String, String[]>();
    map.put("1", new String[] { "a", "b", "c" });
    map.put("2", new String[] { "c", "d", "e" });
    map.put("3", new String[] { "f", "g", "h" });

        String in = "12";

        List<String> ret =  mix(in,map);
        for(int i=0;i<ret.size();i++) System.out.println(ret.get(i));
        }
}

- Anonymous November 19, 2017 | Flag Reply
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of 0 vote

import java.util.List;
import java.util.Vector;
import java.util.Map;
import java.util.HashMap;

public class Mixer {

 public static List<String> mix(String in, Map<String, String[]> map) {
        List<String> combs = new Vector<String>();
        int indexes[] = new int[in.length()];

        do {
                String word="";
                for(int i=0;i<in.length();i++) word += map.get(Character.toString(in.charAt(i)))[indexes[i]];
                combs.add(word);
        } while(increment(indexes,0) == 0);

        return combs;
}

 private static int increment(int[] indexes, int order) {
        if(order == indexes.length -1 && indexes[order]==2) return -1;
        if(++indexes[order] == 3)
        {
           indexes[order]=0;
           return increment(indexes, ++order);
        }
        return 0;
}

 public static void main(String args[]) {
        Map<String, String[]> map = new HashMap<String, String[]>();
    map.put("1", new String[] { "a", "b", "c" });
    map.put("2", new String[] { "c", "d", "e" });
    map.put("3", new String[] { "f", "g", "h" });

        String in = "12";

        List<String> ret =  mix(in,map);
        for(int i=0;i<ret.size();i++) System.out.println(ret.get(i));
        }
}

- thatfernando@yahoo.com November 19, 2017 | Flag Reply
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of 0 vote

This will work for any input , not just for "12"

private static void printAllCombos(String query, Map map) {
        char[] arr = query.toCharArray();
        Set result = new HashSet<>();
        for(int a = 0; a < arr.length ; a++) {
            for(int b=a+1; b < arr.length; b++) {
                String[] a1 = (String[]) map.get(String.valueOf(arr[a]));
                String[] a2 = (String[]) map.get(String.valueOf(arr[b]));
                for(int c = 0; c < a1.length ; c++) {
                    for (int d = 0; d < a2.length; d++) {
                        result.add(a1[c]+a2[d]);
                    }
                }

            }
        }

        Iterator<String> it = result.iterator();
        while(it.hasNext()) {
            System.out.println(it.next());
        }
    }

- nandinicbit November 19, 2017 | Flag Reply


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