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SamTheKoreanSamTheKorean
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Merge pull request #580 from HC-kang/main
[강희찬] WEEK 13 Solution
2 parents e4ac6b1 + a1adfa1 commit 89b1053

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‎find-median-from-data-stream/HC-kang.ts

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/**
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* https://leetcode.com/problems/find-median-from-data-stream
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* array with binary search
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*/
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class MedianFinder {
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// S.C. O(n)
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private nums: number[] = [];
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// T.C. O(n)
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addNum(num: number): void {
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if (this.nums.length === 0) {
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this.nums.push(num);
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return;
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} else {
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this.putNumWithBinarySearch(num);
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}
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}
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private putNumWithBinarySearch(num: number): void {
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let left = 0;
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let right = this.nums.length - 1;
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while (left <= right) {
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const mid = Math.floor((left + right) / 2);
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if (this.nums[mid] === num) {
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this.nums.splice(mid, 0, num);
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return;
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} else if (this.nums[mid] < num) {
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left = mid + 1;
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} else {
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right = mid - 1;
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}
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}
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// T.C. O(n)
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this.nums.splice(left, 0, num);
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}
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// T.C. O(1)
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findMedian(): number {
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const len = this.nums.length;
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if (len % 2 === 1) {
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return this.nums[Math.floor(len / 2)];
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} else {
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return (this.nums[len / 2] + this.nums[len / 2 - 1]) / 2;
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}
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}
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}
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/**
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* heap...
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* TL;DR
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*/
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class MedianFinder {
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// S.C. O(n)
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private smallHalf: MaxHeap = new MaxHeap();
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private largeHalf: MinHeap = new MinHeap();
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// T.C. O(log n)
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addNum(num: number): void {
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this.smallHalf.push(num);
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this.largeHalf.push(this.smallHalf.pop()!);
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if (this.smallHalf.size() < this.largeHalf.size()) {
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this.smallHalf.push(this.largeHalf.pop()!);
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}
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}
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// T.C. O(1)
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findMedian(): number {
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if (this.smallHalf.size() === this.largeHalf.size()) {
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return (this.smallHalf.peek()! + this.largeHalf.peek()!) / 2;
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} else {
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return this.smallHalf.peek()!;
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}
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}
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}
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class MinHeap {
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protected heap: number[] = [];
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push(val: number): void {
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this.heap.push(val);
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this.heapifyUp();
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}
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pop(): number | undefined {
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if (this.heap.length === 0) return undefined;
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if (this.heap.length === 1) return this.heap.pop();
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const result = this.heap[0];
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this.heap[0] = this.heap.pop()!;
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this.heapifyDown();
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return result;
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}
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peek(): number | undefined {
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return this.heap[0];
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}
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size(): number {
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return this.heap.length;
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}
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private heapifyUp(): void {
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let index = this.heap.length - 1;
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while (index > 0) {
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const parentIndex = Math.floor((index - 1) / 2);
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if (this.heap[parentIndex] <= this.heap[index]) break;
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this.swap(parentIndex, index);
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index = parentIndex;
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}
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}
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private heapifyDown(): void {
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let index = 0;
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while (true) {
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let smallest = index;
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const leftChild = 2 * index + 1;
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const rightChild = 2 * index + 2;
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if (
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leftChild < this.heap.length &&
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this.heap[leftChild] < this.heap[smallest]
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) {
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smallest = leftChild;
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}
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if (
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rightChild < this.heap.length &&
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this.heap[rightChild] < this.heap[smallest]
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) {
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smallest = rightChild;
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}
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if (smallest === index) break;
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this.swap(index, smallest);
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index = smallest;
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}
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}
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protected swap(i: number, j: number): void {
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[this.heap[i], this.heap[j]] = [this.heap[j], this.heap[i]];
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}
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}
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class MaxHeap extends MinHeap {
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push(val: number): void {
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super.push(-val);
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}
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pop(): number | undefined {
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const val = super.pop();
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return val === undefined ? undefined : -val;
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}
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peek(): number | undefined {
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const val = super.peek();
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return val === undefined ? undefined : -val;
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}
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}

‎house-robber/HC-kang.ts

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/**
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* https://leetcode.com/problems/house-robber
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* T.C. O(n)
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* S.C. O(1)
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*/
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function rob(nums: number[]): number {
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let prev = 0;
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let curr = 0;
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for (let i = 0; i < nums.length; i++) {
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const temp = curr;
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curr = Math.max(prev + nums[i], curr);
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prev = temp;
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}
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return curr;
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}

‎lowest-common-ancestor-of-a-binary-search-tree/HC-kang.ts

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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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* https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/description
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* T.C. O(log n)
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* S.C. O(log n)
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*/
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function lowestCommonAncestor(
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root: TreeNode | null,
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p: TreeNode | null,
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q: TreeNode | null
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): TreeNode | null {
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if (!root) return null;
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if (root.val > p!.val && root.val > q!.val) {
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return lowestCommonAncestor(root.left, p, q);
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} else if (root.val < p!.val && root.val < q!.val) {
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return lowestCommonAncestor(root.right, p, q);
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} else {
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return root;
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}
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}
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/**
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* iterative
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* T.C. O(log n)
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* S.C. O(1)
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*/
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function lowestCommonAncestor(
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root: TreeNode | null,
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p: TreeNode | null,
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q: TreeNode | null
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): TreeNode | null {
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while (root) {
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if (root.val > p!.val && root.val > q!.val) {
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root = root.left;
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} else if (root.val < p!.val && root.val < q!.val) {
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root = root.right;
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} else {
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return root;
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}
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}
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return null;
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}

‎meeting-rooms/HC-kang.ts

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/**
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* https://leetcode.com/problems/meeting-rooms
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* T.C. O(nlogn)
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* S.C. O(1)
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*/
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function canAttendMeetings(intervals: number[][]): boolean {
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intervals.sort((a, b) => a[0] - b[0]);
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for (let i = 0; i < intervals.length - 1; i++) {
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if (intervals[i][1] > intervals[i + 1][0]) return false;
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}
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return true;
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}

‎non-overlapping-intervals/HC-kang.ts

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/**
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* https://leetcode.com/problems/non-overlapping-intervals
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* T.C. O(n logn)
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* S.C. O(1)
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*
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* [[1,2],[2,3],[3,4],[1,3]] =(sort by end)=> [[1,2],[2,3],[1,3],[3,4]]
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*
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* 0 1 2 3 4...
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* [=) pass
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* [=) pass
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* [===) count++
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* ^^^
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* [=) pass
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*/
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function eraseOverlapIntervals(intervals: number[][]): number {
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intervals.sort((a, b) => a[1] - b[1]);
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let count = 0;
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let end = -Infinity;
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for (let i = 0; i < intervals.length; i++) {
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if (intervals[i][0] < end) { //
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count++;
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} else {
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end = intervals[i][1];
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}
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}
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return count;
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}

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