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Merge pull request #1951 from hyer0705/main
[hyer0705] WEEK 14 Solutions
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‎binary-tree-level-order-traversal/hyer0705.ts‎

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/**
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* Definition for a binary tree node.
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* class TreeNode {
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* val: number
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* left: TreeNode | null
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* right: TreeNode | null
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* constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
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* this.val = (val===undefined ? 0 : val)
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* this.left = (left===undefined ? null : left)
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* this.right = (right===undefined ? null : right)
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* }
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* }
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*/
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// ----- [Solution 1]
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// Time Complexity: O(n)
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// Space Complexity: O(n)
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function levelOrder(root: TreeNode | null): number[][] {
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if (!root) return [];
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const answer: number[][] = [];
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const queue: [TreeNode, number][] = [];
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let pointer = 0;
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queue.push([root, 0]);
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while (pointer < queue.length) {
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const [currNode, level] = queue[pointer++];
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if (!answer[level]) answer[level] = [];
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answer[level].push(currNode.val);
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if (currNode.left) queue.push([currNode.left, level + 1]);
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if (currNode.right) queue.push([currNode.right, level + 1]);
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}
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return answer;
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}
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// ----- [Solution 2]
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// Time Complexity: O(n)
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// Space Complexity: O(n)
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function levelOrder(root: TreeNode | null): number[][] {
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if (!root) return [];
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const answer: number[][] = [];
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const queue: TreeNode[] = [];
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queue.push(root);
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let pointer = 0;
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while (pointer < queue.length) {
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const levelSize = queue.length - pointer;
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const currentLevel: number[] = [];
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for (let i = 0; i < levelSize; i++) {
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const currNode = queue[pointer++];
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currentLevel.push(currNode.val);
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if (currNode.left) queue.push(currNode.left);
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if (currNode.right) queue.push(currNode.right);
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}
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answer.push(currentLevel);
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}
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return answer;
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}

‎counting-bits/hyer0705.ts‎

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// Time Complexity: O(n)
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// Space Complexity: O(n)
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function countBits(n: number): number[] {
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const ans: number[] = Array.from({ length: n + 1 }, () => 0);
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for (let i = 1; i <= n; i++) {
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ans[i] = ans[i >> 1] + (i & 1);
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}
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return ans;
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}

‎house-robber-ii/hyer0705.ts‎

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// Time Complexity: O(n)
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// Space Complexity: O(1)
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function rob(nums: number[]): number {
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const n = nums.length;
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if (n === 1) return nums[0];
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if (n === 2) return Math.max(nums[0], nums[1]);
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const getLinearRob = (start: number, end: number) => {
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let prev2 = 0;
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let prev1 = 0;
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for (let i = start; i <= end; i++) {
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const current = Math.max(prev1, prev2 + nums[i]);
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prev2 = prev1;
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prev1 = current;
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}
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return prev1;
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};
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let case1 = getLinearRob(0, n - 2);
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let case2 = getLinearRob(1, n - 1);
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return Math.max(case1, case2);
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}

‎meeting-rooms-ii/hyer0705.ts‎

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import { Interval } from "../home/lib/index";
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/**
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* Definition of Interval:
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* export class Interval {
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* start :number;
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* end :number;
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* constructor(start :number, end :number) {
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* this.start = start;
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* this.end = end;
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* }
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* }
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*/
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import { MinHeap } from "@datastructures-js/heap";
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export class Solution {
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/**
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* @param intervals: an array of meeting time intervals
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* @return: the minimum number of conference rooms required
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*/
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// Time Complexity: O(n log n)
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// Space Complexity: O(n)
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minMeetingRooms(intervals: Interval[]): number {
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intervals.sort((a, b) => a.start - b.start);
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const minHeap = new MinHeap();
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const n = intervals.length;
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let maximumRooms = 0;
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for (let i = 0; i < n; i++) {
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const { start, end } = intervals[i];
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if (minHeap.isEmpty()) {
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minHeap.insert(end);
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maximumRooms = Math.max(maximumRooms, minHeap.size());
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continue;
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}
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if (start >= minHeap.root()) {
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minHeap.pop();
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}
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minHeap.insert(end);
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maximumRooms = Math.max(maximumRooms, minHeap.size());
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}
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return maximumRooms;
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}
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}

‎word-search-ii/hyer0705.ts‎

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// 84ms
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class TrieNode {
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children: Map<string, TrieNode>;
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isEndOf: boolean;
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word: string | null;
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constructor() {
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this.children = new Map();
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this.word = null;
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}
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}
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class Trie {
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root: TrieNode;
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constructor() {
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this.root = new TrieNode();
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}
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insert(word: string) {
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let current = this.root;
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for (const char of word) {
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if (!current.children.has(char)) {
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current.children.set(char, new TrieNode());
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}
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current = current.children.get(char);
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}
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current.word = word;
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}
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}
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function findWords(board: string[][], words: string[]): string[] {
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const m = board.length;
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const n = board[0].length;
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const dictionary = new Trie();
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for (const word of words) {
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dictionary.insert(word);
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}
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const results: string[] = [];
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const dfs = (row: number, col: number, trieNode: TrieNode) => {
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if (trieNode.word !== null) {
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results.push(trieNode.word);
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trieNode.word = null;
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}
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const directions = [
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[-1, 0],
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[1, 0],
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[0, -1],
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[0, 1],
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];
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for (const [dr, dc] of directions) {
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const [nr, nc] = [row + dr, col + dc];
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if (nr >= 0 && nr < m && nc >= 0 && nc < n) {
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if (trieNode.children.has(board[nr][nc])) {
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const char = board[nr][nc];
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const childNode = trieNode.children.get(char);
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if (board[nr][nc] !== "#") {
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board[nr][nc] = "#";
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dfs(nr, nc, trieNode.children.get(char));
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board[nr][nc] = char;
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}
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if (childNode.children.size === 0 && childNode.word === null) {
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trieNode.children.delete(char);
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}
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}
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}
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}
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};
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for (let i = 0; i < m; i++) {
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for (let j = 0; j < n; j++) {
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const firstChar = board[i][j];
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if (dictionary.root.children.has(firstChar)) {
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board[i][j] = "#";
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dfs(i, j, dictionary.root.children.get(firstChar));
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board[i][j] = firstChar;
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}
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}
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}
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return results;
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}
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// 2312ms
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class TrieNode {
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children: Map<string, TrieNode>;
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word: string | null;
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constructor() {
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this.children = new Map();
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this.word = null;
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}
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}
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class Trie {
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root: TrieNode;
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constructor() {
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this.root = new TrieNode();
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}
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insert(word: string) {
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let current = this.root;
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for (const char of word) {
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if (!current.children.has(char)) {
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current.children.set(char, new TrieNode());
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}
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current = current.children.get(char)!;
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}
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current.word = word;
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}
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}
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function findWords(board: string[][], words: string[]): string[] {
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const m = board.length;
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const n = board[0].length;
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const dictionary = new Trie();
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for (const word of words) {
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dictionary.insert(word);
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}
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const results: string[] = [];
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const dfs = (row: number, col: number, trieNode: TrieNode, path: string) => {
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if (trieNode.word === path) {
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results.push(path);
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trieNode.word = null;
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}
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const directions = [
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[-1, 0],
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[1, 0],
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[0, -1],
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[0, 1],
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];
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for (const [dr, dc] of directions) {
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const [nr, nc] = [row + dr, col + dc];
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if (nr >= 0 && nr < m && nc >= 0 && nc < n) {
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if (trieNode.children.has(board[nr][nc])) {
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if (!isVisited.has(`${nr},${nc}`)) {
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isVisited.add(`${nr},${nc}`);
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dfs(nr, nc, trieNode.children.get(board[nr][nc])!, path + board[nr][nc]);
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isVisited.delete(`${nr},${nc}`);
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}
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}
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}
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}
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};
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const isVisited = new Set<string>(); // 'r,c'
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for (let i = 0; i < m; i++) {
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for (let j = 0; j < n; j++) {
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const firstChar = board[i][j];
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if (dictionary.root.children.has(firstChar)) {
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isVisited.add(`${i},${j}`);
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dfs(i, j, dictionary.root.children.get(firstChar)!, firstChar);
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isVisited.delete(`${i},${j}`);
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}
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}
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}
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return results;
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}

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