Print all valid words that are possible using Characters of Array

Given a dictionary and a character array, print all valid words that are possible using characters from the array. 
Examples: 

Input : Dict - {"go","bat","me","eat","goal", 
                                "boy", "run"} 
        arr[] = {'e','o','b', 'a','m','g', 'l'} 
Output : go, me, goal. 

Asked In : Microsoft Interview

The idea is to use Trie data structure to store dictionary, then search words in Trie using characters of given array. 

1. Create an empty Trie and insert all words of given dictionary into the Trie.
2. After that, we have pick only those characters in ‘Arr[]’ which are a child of the root of Trie.
3. To quickly find whether a character is present in array or not, we create a hash of character arrays.

Below is the implementation of above idea 

C++

// C++ program to print all valid words that
// are possible using character of array
#include<bits/stdc++.h>
using namespace std;

// Converts key current character into index
// use only 'a' through 'z'
#define char_int(c) ((int)c - (int)'a')

//converts current integer into character
#define int_to_char(c) ((char)c + (char)'a')

// Alphabet size
#define SIZE (26)

// trie Node
struct TrieNode
{
    TrieNode *Child[SIZE];

    // isLeaf is true if the node represents
    // end of a word
    bool leaf;
};

// Returns new trie node (initialized to NULLs)
TrieNode *getNode()
{
    TrieNode * newNode = new TrieNode;
    newNode->leaf = false;
    for (int i =0 ; i< SIZE ; i++)
        newNode->Child[i] = NULL;
    return newNode;
}

// If not present, inserts key into trie
// If the key is prefix of trie node, just
// marks leaf node
void insert(TrieNode *root, char *Key)
{
    int n = strlen(Key);
    TrieNode * pChild = root;

    for (int i=0; i<n; i++)
    {
        int index = char_int(Key[i]);

        if (pChild->Child[index] == NULL)
            pChild->Child[index] = getNode();

        pChild = pChild->Child[index];
    }

    // make last node as leaf node
    pChild->leaf = true;
}

// A recursive function to print all possible valid
// words present in array
void searchWord(TrieNode *root, bool Hash[], string str)
{
    // if we found word in trie / dictionary
    if (root->leaf == true)
        cout << str << endl ;

    // traverse all child's of current root
    for (int K =0; K < SIZE; K++)
    {
        if (Hash[K] == true && root->Child[K] != NULL )
        {
            // add current character
            char c = int_to_char(K);

            // Recursively search reaming character of word
            // in trie
            searchWord(root->Child[K], Hash, str + c);
        }
    }
}

// Prints all words present in dictionary.
void PrintAllWords(char Arr[], TrieNode *root, int n)
{
    // create a 'has' array that will store all present
    // character in Arr[]
    bool Hash[SIZE];

    for (int i = 0 ; i < n; i++)
        Hash[char_int(Arr[i])] = true;

    // temporary node
    TrieNode *pChild = root ;

    // string to hold output words
    string str = "";

    // Traverse all matrix elements. There are only 26
    // character possible in char array
    for (int i = 0 ; i < SIZE ; i++)
    {
        // we start searching for word in dictionary
        // if we found a character which is child
        // of Trie root
        if (Hash[i] == true && pChild->Child[i] )
        {
            str = str+(char)int_to_char(i);
            searchWord(pChild->Child[i], Hash, str);
            str = "";
        }
    }
}

//Driver program to test above function
int main()
{
    // Let the given dictionary be following
    char Dict[][20] = {"go", "bat", "me", "eat",
                       "goal", "boy", "run"} ;

    // Root Node of Trie
    TrieNode *root = getNode();

    // insert all words of dictionary into trie
    int n = sizeof(Dict)/sizeof(Dict[0]);
    for (int i=0; i<n; i++)
        insert(root, Dict[i]);

    char arr[] = {'e', 'o', 'b', 'a', 'm', 'g', 'l'} ;
    int N = sizeof(arr)/sizeof(arr[0]);

    PrintAllWords(arr, root, N);

    return 0;
}

Java

// Java program to print all valid words that
// are possible using character of array
public class SearchDict_charArray {

    // Alphabet size
    static final int SIZE = 26;

    // trie Node
    static class TrieNode
    {
        TrieNode[] Child = new TrieNode[SIZE];

        // isLeaf is true if the node represents
        // end of a word
        boolean leaf;

        // Constructor
        public TrieNode() {
            leaf = false;
            for (int i =0 ; i< SIZE ; i++)
                    Child[i] = null;
        }
    }

    // If not present, inserts key into trie
    // If the key is prefix of trie node, just
    // marks leaf node
    static void insert(TrieNode root, String Key)
    {
        int n = Key.length();
        TrieNode pChild = root;

        for (int i=0; i<n; i++)
        {
            int index = Key.charAt(i) - 'a';

            if (pChild.Child[index] == null)
                pChild.Child[index] = new TrieNode();

            pChild = pChild.Child[index];
        }

        // make last node as leaf node
        pChild.leaf = true;
    }

    // A recursive function to print all possible valid
    // words present in array
    static void searchWord(TrieNode root, boolean Hash[],
                                            String str)
    {
        // if we found word in trie / dictionary
        if (root.leaf == true)
            System.out.println(str);

        // traverse all child's of current root
        for (int K =0; K < SIZE; K++)
        {
            if (Hash[K] == true && root.Child[K] != null )
            {
                // add current character
                char c = (char) (K + 'a');

                // Recursively search reaming character
                // of word in trie
                searchWord(root.Child[K], Hash, str + c);
            }
        }
    }

    // Prints all words present in dictionary.
    static void PrintAllWords(char Arr[], TrieNode root,
                                              int n)
    {
        // create a 'has' array that will store all
        // present character in Arr[]
        boolean[] Hash = new boolean[SIZE];

        for (int i = 0 ; i < n; i++)
            Hash[Arr[i] - 'a'] = true;

        // temporary node
        TrieNode pChild = root ;

        // string to hold output words
        String str = "";

        // Traverse all matrix elements. There are only
        // 26 character possible in char array
        for (int i = 0 ; i < SIZE ; i++)
        {
            // we start searching for word in dictionary
            // if we found a character which is child
            // of Trie root
            if (Hash[i] == true && pChild.Child[i] != null )
            {
                str = str+(char)(i + 'a');
                searchWord(pChild.Child[i], Hash, str);
                str = "";
            }
        }
    }

    //Driver program to test above function
    public static void main(String args[])
    {
        // Let the given dictionary be following
        String Dict[] = {"go", "bat", "me", "eat",
                           "goal", "boy", "run"} ;

        // Root Node of Trie
        TrieNode root = new TrieNode();

        // insert all words of dictionary into trie
        int n = Dict.length;
        for (int i=0; i<n; i++)
            insert(root, Dict[i]);

        char arr[] = {'e', 'o', 'b', 'a', 'm', 'g', 'l'} ;
        int N = arr.length;

        PrintAllWords(arr, root, N);
    }
}
// This code is contributed by Sumit Ghosh

C#

// C# program to print all valid words that
// are possible using character of array
using System;

public class SearchDict_charArray
{

    // Alphabet size
    static readonly int SIZE = 26;

    // trie Node
    public class TrieNode
    {
        public TrieNode[] Child = new TrieNode[SIZE];

        // isLeaf is true if the node represents
        // end of a word
        public Boolean leaf;

        // Constructor
        public TrieNode()
        {
            leaf = false;
            for (int i =0 ; i< SIZE ; i++)
                    Child[i] = null;
        }
    }

    // If not present, inserts key into trie
    // If the key is prefix of trie node, just
    // marks leaf node
    static void insert(TrieNode root, String Key)
    {
        int n = Key.Length;
        TrieNode pChild = root;

        for (int i = 0; i < n; i++)
        {
            int index = Key[i] - 'a';

            if (pChild.Child[index] == null)
                pChild.Child[index] = new TrieNode();

            pChild = pChild.Child[index];
        }

        // make last node as leaf node
        pChild.leaf = true;
    }

    // A recursive function to print all possible valid
    // words present in array
    static void searchWord(TrieNode root, Boolean []Hash,
                                            String str)
    {
        // if we found word in trie / dictionary
        if (root.leaf == true)
            Console.WriteLine(str);

        // traverse all child's of current root
        for (int K = 0; K < SIZE; K++)
        {
            if (Hash[K] == true && root.Child[K] != null )
            {
                // add current character
                char c = (char) (K + 'a');

                // Recursively search reaming character
                // of word in trie
                searchWord(root.Child[K], Hash, str + c);
            }
        }
    }

    // Prints all words present in dictionary.
    static void PrintAllWords(char []Arr, TrieNode root,
                                            int n)
    {
        // create a 'has' array that will store all
        // present character in Arr[]
        Boolean[] Hash = new Boolean[SIZE];

        for (int i = 0 ; i < n; i++)
            Hash[Arr[i] - 'a'] = true;

        // temporary node
        TrieNode pChild = root ;

        // string to hold output words
        String str = "";

        // Traverse all matrix elements. There are only
        // 26 character possible in char array
        for (int i = 0 ; i < SIZE ; i++)
        {
            // we start searching for word in dictionary
            // if we found a character which is child
            // of Trie root
            if (Hash[i] == true && pChild.Child[i] != null )
            {
                str = str+(char)(i + 'a');
                searchWord(pChild.Child[i], Hash, str);
                str = "";
            }
        }
    }

    // Driver code
    public static void Main(String []args)
    {
        // Let the given dictionary be following
        String []Dict = {"go", "bat", "me", "eat",
                        "goal", "boy", "run"} ;

        // Root Node of Trie
        TrieNode root = new TrieNode();

        // insert all words of dictionary into trie
        int n = Dict.Length;
        for (int i = 0; i < n; i++)
            insert(root, Dict[i]);

        char []arr = {'e', 'o', 'b', 'a', 'm', 'g', 'l'} ;
        int N = arr.Length;

        PrintAllWords(arr, root, N);
    }
}

/* This code is contributed by PrinciRaj1992 */

Output:

go
goal
me

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