Boggle | Set 2 (Using Trie)

Given a dictionary, a method to do lookup in dictionary and a M x N board where every cell has one character. Find all possible words that can be formed by a sequence of adjacent characters. Note that we can move to any of 8 adjacent characters, but a word should not have multiple instances of same cell.


Input: dictionary[] = {"GEEKS", "FOR", "QUIZ", "GO"};
       boggle[][]   = {{'G','I','Z'},
      isWord(str): returns true if str is present in dictionary
                   else false.

Output:  Following words of dictionary are present


We have discussed a Graph DFS based solution in below post.
Boggle (Find all possible words in a board of characters) | Set 1

Here we discus Trie based solution which is better then DFS base solution.
Given Dictionary dictionary[] = {“GEEKS”, “FOR”, “QUIZ”, “GO”}
1. Create an Empty trie and insert all words of given dictionary into trie

      After insertion Tre look like (leaf nodes are in RED )
                    /   \    \
                    G   F     Q
                 /  |   |     |
                O   E   O     U
                    |   |     |
                    E    R     I
                    |         |  
                    K         Z 

2. After that we have pick only those character in boggle[][] which are child of root of Trie
Let for above we pick ‘G’ boggle[0][0] , ‘Q’ boggle[2][0] (they both are present in boggle matrix)
3. search a word in a trie which start with character that we pick in step 2

1) Create bool visited boolean matrix (Visited[M][N] = false )
2) Call SearchWord() for every cell (i, j) which has one of the
   the first characters of dictionary words. In above example,
   we have 'G' and 'Q' as first characters.

SearchWord(Trie *root, i, j, visited[][N])
if root->leaf == true 
   print word 

if we seen this element first time then make it visited.
   visited[i][j] = true
      traverse all child of current root 
      k goes (0 to 26 ) [there are only 26 Alphabet] 
      add current char and search for next character 

      find next character which is adjacent to boggle[i][j]
      they are 8 adjacent cells of boggle[i][j] (i+1, j+1), 
      (i+1, j) (i-1, j) and so on.
   make it unvisited visited[i][j] = false 

Below is c++ implementation of above idea

// C++ program for Boggle game
using namespace std;

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

// Alphabet size
#define SIZE (26)

#define M 3
#define N 3

// 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;

// function to check that current location
// (i and j) is in matrix range
bool isSafe(int i, int j, bool visited[M][N])
    return (i >=0 && i < M && j >=0 &&
            j < N && !visited[i][j]);

// A recursive function to print all words present on boggle
void searchWord(TrieNode *root, char boggle[M][N], int i,
                int j, bool visited[][N], string str)
    // if we found word in trie / dictionary
    if (root->leaf == true)
        cout << str << endl ;

    // If both I and j in  range and we visited
    // that element of matrix first time
    if (isSafe(i, j, visited))
        // make it visited
        visited[i][j] = true;

        // traverse all childs of current root
        for (int K =0; K < SIZE; K++)
            if (root->Child[K] != NULL)
                // current character
                char ch = (char)K + (char)'A' ;

                // Recursively search reaming character of word
                // in trie for all 8 adjacent cells of boggle[i][j]
                if (isSafe(i+1,j+1,visited) && boggle[i+1][j+1] == ch)
                if (isSafe(i, j+1,visited)  && boggle[i][j+1] == ch)
                    searchWord(root->Child[K],boggle,i, j+1,visited,str+ch);
                if (isSafe(i-1,j+1,visited) && boggle[i-1][j+1] == ch)
                    searchWord(root->Child[K],boggle,i-1, j+1,visited,str+ch);
                if (isSafe(i+1,j, visited)  && boggle[i+1][j] == ch)
                    searchWord(root->Child[K],boggle,i+1, j,visited,str+ch);
                if (isSafe(i+1,j-1,visited) && boggle[i+1][j-1] == ch)
                    searchWord(root->Child[K],boggle,i+1, j-1,visited,str+ch);
                if (isSafe(i, j-1,visited)&& boggle[i][j-1] == ch)
                if (isSafe(i-1,j-1,visited) && boggle[i-1][j-1] == ch)
                    searchWord(root->Child[K],boggle,i-1, j-1,visited,str+ch);
                if (isSafe(i-1, j,visited) && boggle[i-1][j] == ch)
                    searchWord(root->Child[K],boggle,i-1, j, visited,str+ch);

        // make current element unvisited
        visited[i][j] = false;

// Prints all words present in dictionary.
void findWords(char boggle[M][N], TrieNode *root)
    // Mark all characters as not visited
    bool visited[M][N];

    TrieNode *pChild = root ;

    string str = "";

    // traverse all matrix elements
    for (int i = 0 ; i < M; i++)
        for (int j = 0 ; j < N ; j++)
            // we start searching for word in dictionary
            // if we found a character which is child
            // of Trie root
            if (pChild->Child[char_int(boggle[i][j])] )
                str = str+boggle[i][j];
                           boggle, i, j, visited, str);
                str = "";

//Driver program to test above function
int main()
    // Let the given dictionary be following
    char *dictionary[] = {"GEEKS", "FOR", "QUIZ", "GEE"};

    // root Node of trie
    TrieNode *root = getNode();

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

    char boggle[M][N] = {{'G','I','Z'},

    findWords(boggle, root);

    return 0;



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