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Commit c0ace54

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Problem : 186, search word in a grid from a dictionary
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‎README.md

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| Current Status| Stats |
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| :------------: | :----------: |
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| Total Problems | 186 |
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| Total Problems | 187 |
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</center>
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| :------------ | :----------: |
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| You are given a digit string (e.g "1234", "567" etc), provide all possible letter combinations we could generate from this digit string, based on the mapping we see on the telphone/mobile dialpad. If you have typed SMS in old style phones, you would know. For e.g. "1" is mapped to "abc", 2 is mapped to "def". You can refer to the <a href="http://techotv.com/wp-content/uploads/2013/03/Lumia-620-dial-pad-screen-1.jpg" target="_blank">image.</a>. <ul><li> Example: "34" will give output: {"dg","dh","di","eg","eh","ei","fg","fh","fi"} </li></ul> Note that order does not matter in result set.|[dialpad_combinations.cpp](backtracking_problems/dialpad_combinations.cpp)|
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| Implement wildcard pattern maching with support for '?' & '*'. <ul><li>'?' Matches any single character.</li></ul><ul><li>'*' Matches any sequence of character.</li></ul>. Checkout examples in file for more details.|[wild_card_matching.cpp](backtracking_problems/wild_card_matching.cpp)|
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| Given a 2D board and list of words from a dictionary, find all the possible words on board fromt the list. (Check example in the solution)| [word_search.cpp](backtracking_problems/word_search.cpp)|
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‎backtracking_problems/word_search.cpp

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/*
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* Given a 2D board and list of words from a dictionary,
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* find all the possible words on board fromt the list.
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* Example:
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* words = ["oath","pea","eat","rain"]
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* board =
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* [
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* ['o','a','a','n'],
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* ['e','t','a','e'],
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* ['i','h','k','r'],
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* ['i','f','l','v']
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* ]
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*
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* Output: ["eat", "oath"]
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*
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* Source : LeetCode Problem 212
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*
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* Approach:
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*
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* We can use backtracking(dfs) to traverse from each character on board
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* to all four direction. In order to do a fast searching, we can use
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* a trie from words in dictionary, as soon as we find a word from dictionary
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* in trie, we remove it from trie, so we don't have duplicates.
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* Also, we can use the board to mark '#' as visited character to
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* achieve backtracking.
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*/
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#include <vector>
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#include <iostream>
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struct TrieNode {
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std::string word;
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std::vector<TrieNode*> children;
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TrieNode():
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word{""}, children{std::vector<TrieNode*>(26, nullptr)}{}
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};
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TrieNode* build_trie(const std::vector<std::string>& dictionary)
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{
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TrieNode* root = new TrieNode();
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for (auto word: dictionary) {
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TrieNode* curr = root;
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for (auto c: word) {
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int index = c - 'a';
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if (curr->children[index] == nullptr) {
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curr->children[index] = new TrieNode();
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}
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curr = curr->children[index];
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}
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curr->word = word;
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}
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return root;
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}
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void backtrack(std::vector<std::vector<char>>& board,
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TrieNode* root, int i, int j, std::vector<std::string>& result)
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{
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char c = board[i][j];
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if (c == '#' || root == nullptr) {
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return;
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}
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int index = c - 'a';
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TrieNode* curr = root->children[index];
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if (curr == nullptr) {
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return;
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}
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if (curr->word != "") {
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result.push_back(curr->word);
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// Reset to avoid duplicates.
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curr->word = "";
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}
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board[i][j] = '#';
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if (i > 0) {
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backtrack(board, curr, i - 1, j, result);
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}
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if (j > 0) {
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backtrack(board, curr, i, j - 1, result);
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}
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if (i < board.size() - 1) {
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backtrack(board, curr, i + 1, j, result);
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}
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if (j < board[0].size() - 1) {
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backtrack(board, curr, i, j + 1, result);
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}
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board[i][j] = c;
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}
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std::vector<std::string> find_words(std::vector<std::vector<char>>& board,
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std::vector<std::string>& dictionary)
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{
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std::vector<std::string> result;
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for (int i = 0; i < board.size(); ++i) {
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for (int j = 0; j < board[0].size(); ++j) {
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TrieNode* root = build_trie(dictionary);
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backtrack(board, root, i, j, result);
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}
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}
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return result;
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}
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template <typename T>
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void print_vector(const std::vector<T>& vec)
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{
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std::cout << "{ ";
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for (auto t : vec) {
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std::cout << t << " ";
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}
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std::cout << " }" << std::endl;
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}
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void print_board(const std::vector<std::vector<char>>& board)
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{
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for (auto v: board) {
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print_vector(v);
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}
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}
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int main()
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{
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std::vector<std::vector<char>> board = {
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{'o','a','a','n'},
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{'e','t','a','e'},
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{'i','h','k','r'},
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{'i','f','l','v'}
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};
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std::vector<std::string> dictionary = {
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"oath","pea","eat","rain"
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};
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std::vector<std::string> result = find_words(board, dictionary);
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std::cout << "Board:" << std::endl;
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print_board(board);
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std::cout << "Dictionary:" << std::endl;
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print_vector(dictionary);
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std::cout << "Result:" << std::endl;
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print_vector(result);
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return 0;
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}

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