add recursion and backtracking and visuals

Author: beck chen

Leetcode Visuals/Recursion and Backtracking.drawio

@@ -0,0 +1 @@
+<mxfile host="Electron" modified="2021-08-26T17:35:43.791Z" agent="5.0 (Macintosh; Intel Mac OS X 11_2_3) AppleWebKit/537.36 (KHTML, like Gecko) draw.io/14.6.13 Chrome/89.0.4389.128 Electron/12.0.7 Safari/537.36" etag="MSLyCtLkK84S1TL8sjfb" version="14.6.13" type="device" pages="2"><diagram id="5uokHB6_kULKvT_LYLOu" name="LC17: Letter Combinations of a Phone 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id="pSCcazf5C_0qfcGw3Gmh" name="LC212: Word Search II">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</diagram></mxfile>

Leetcode Visuals/Trees and Graphs.drawio

@@ -0,0 +1,45 @@
+/**
+ * @param {string} digits
+ * @return {string[]}
+ */
+var letterCombinations = function (digitsAsStr) {
+    if (!digitsAsStr || digitsAsStr.length === 0) { return []; }
+    const combinations = [];
+    let buffer = '';
+    let digitIndex = 0;
+    traverse(digitsAsStr, buffer, digitIndex, combinations);
+
+    return combinations;
+};
+
+function traverse(digitsAsStr, buffer, digitIndex, combinations) {
+    if (digitIndex === digitsAsStr.length) {
+        combinations.push(buffer);
+        return;
+    }
+
+    const currentDigit = digitsAsStr[digitIndex];
+    if (currentDigit === '0' || currentDigit === '1') {
+        traverse(digitsAsStr, buffer, digitIndex + 1, combinations);
+    } else {
+        const charsAsStr = getCharsFromDigit(currentDigit);
+        for (let charIndex = 0; charIndex < charsAsStr.length; charIndex++) {
+            traverse(digitsAsStr, buffer + charsAsStr[charIndex], digitIndex + 1, combinations);
+        }
+    }
+}
+
+function getCharsFromDigit(digit) {
+    const digitToCharsMap = {
+        '2': 'abc',
+        '3': 'def',
+        '4': 'ghi',
+        '5': 'jkl',
+        '6': 'mno',
+        '7': 'pqrs',
+        '8': 'tuv',
+        '9': 'wxyz'
+    };
+
+    return digitToCharsMap[digit];
+}

leetcode practice/recursion and backtracking/letterCombinationsOfAPhoneNumber.js

@@ -0,0 +1,63 @@
+/**
+ * @param {character[][]} board
+ * @param {string[]} words
+ * @return {string[]}
+ */
+var findWords = function (board, words) {
+    const rootTrieNode = buildTrie(words);
+
+    const numRows = board.length, numCols = board[0].length;
+    const collection = new Set();
+    for (let rowIndex = 0; rowIndex < numRows; rowIndex++) {
+        for (let colIndex = 0; colIndex < numCols; colIndex++) {
+            searchWord(rootTrieNode, board, rowIndex, colIndex, collection);
+        }
+    }
+
+    return [...collection];
+};
+
+function searchWord(parentNode, board, rowIndex, colIndex, collection) {
+    if (!board[rowIndex] || !board[rowIndex][colIndex]) { return; }
+
+    const tempChar = board[rowIndex][colIndex];
+    board[rowIndex][colIndex] = '$';
+    const currentNode = parentNode.children[tempChar];
+    if (currentNode) {
+        if (currentNode.word) {
+            collection.add(currentNode.word);
+        }
+        searchWord(currentNode, board, rowIndex + 1, colIndex, collection);
+        searchWord(currentNode, board, rowIndex - 1, colIndex, collection);
+        searchWord(currentNode, board, rowIndex, colIndex + 1, collection);
+        searchWord(currentNode, board, rowIndex, colIndex - 1, collection);
+    }
+
+    board[rowIndex][colIndex] = tempChar;
+}
+
+function buildTrie(wordsArr) {
+    const root = new TrieNode();
+
+    for (let word of wordsArr) {
+        let currentNode = root;
+        for (let charIndex = 0; charIndex < word.length; charIndex++) {
+            const currentChar = word[charIndex];
+            if (!currentNode.children[currentChar]) {
+                currentNode.children[currentChar] = new TrieNode();
+            }
+
+            currentNode = currentNode.children[currentChar];
+        }
+
+        currentNode.word = word;
+    }
+
+    return root;
+}
+
+class TrieNode {
+    constructor() {
+        this.children = {};
+    }
+}