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Merge pull request #1612 from Jeehay28/main
[Jeehay28] WEEK 13 Solutions
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‎find-median-from-data-stream/Jeehay28.ts

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class MedianFinder {
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// [1, 2, 3, 4, 5, 6]
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private lower: MaxHeap; // max heap [3, 2, 1]
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private upper: MinHeap; // min heap [4, 5, 6]
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constructor() {
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this.upper = new MinHeap();
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this.lower = new MaxHeap();
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}
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// TC: O(log n)
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// SC: O(n)
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addNum(num: number): void {
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if (this.upper.size() === 0 || this.upper.getRoot() <= num) {
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this.upper.insert(num);
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} else {
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this.lower.insert(num);
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}
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// Balance
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if (this.lower.size() - this.upper.size() > 1) {
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this.upper.insert(this.lower.removeRoot());
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} else if (this.upper.size() - this.lower.size() > 1) {
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this.lower.insert(this.upper.removeRoot());
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}
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}
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// TC: O(1)
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// SC: O(1)
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findMedian(): number {
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if (this.upper.size() === this.lower.size()) {
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return (this.upper.getRoot() + this.lower.getRoot()) / 2;
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} else if (this.upper.size() > this.lower.size()) {
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return this.upper.getRoot();
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} else {
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return this.lower.getRoot();
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}
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}
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}
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/**
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* Your MedianFinder object will be instantiated and called as such:
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* var obj = new MedianFinder()
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* obj.addNum(num)
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* var param_2 = obj.findMedian()
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*/
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class MinHeap {
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private heap: number[] = [];
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size(): number {
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return this.heap.length;
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}
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getRoot(): number {
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return this.heap[0];
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}
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insert(num: number): void {
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this.heap.push(num);
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this.bubbleUp();
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}
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removeRoot(): number {
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const top = this.heap[0];
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const end = this.heap.pop()!;
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if (this.heap.length > 0) {
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this.heap[0] = end;
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this.bubbleDown();
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}
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return top;
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}
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// Fix after removal (downward)
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bubbleDown(): void {
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let idx = 0;
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const length = this.heap.length;
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const val = this.heap[0];
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while (true) {
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let leftIdx = 2 * idx + 1;
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let rightIdx = 2 * idx + 2;
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let swap = idx;
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if (leftIdx < length && this.heap[leftIdx] < this.heap[swap]) {
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swap = leftIdx;
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}
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if (rightIdx < length && this.heap[rightIdx] < this.heap[swap]) {
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swap = rightIdx;
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}
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if (swap === idx) break;
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this.heap[idx] = this.heap[swap];
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this.heap[swap] = val;
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idx = swap;
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}
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}
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// Fix after insert (upward)
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bubbleUp(): void {
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let idx = this.heap.length - 1;
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const val = this.heap[idx];
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// Heap as an array
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// left child: 2 * i + 1
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// right child: 2 * i + 2
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// parent: Math.floor((i-1) / 2)
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while (idx > 0) {
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const parentIdx = Math.floor((idx - 1) / 2);
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const parent = this.heap[parentIdx];
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if (val >= parent) break;
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this.heap[parentIdx] = val;
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this.heap[idx] = parent;
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idx = parentIdx;
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}
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}
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}
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class MaxHeap {
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private heap: number[] = [];
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size(): number {
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return this.heap.length;
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}
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getRoot(): number {
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return this.heap[0];
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}
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insert(num: number): void {
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this.heap.push(num);
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this.bubbleUp();
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}
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removeRoot(): number {
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const top = this.heap[0];
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const end = this.heap.pop()!;
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if (this.heap.length > 0) {
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this.heap[0] = end;
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this.bubbleDown();
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}
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return top;
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}
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bubbleDown(): void {
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let idx = 0;
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const length = this.heap.length;
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const val = this.heap[0];
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while (true) {
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let leftIdx = 2 * idx + 1;
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let rightIdx = 2 * idx + 2;
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let swap = idx;
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if (leftIdx < length && this.heap[leftIdx] > this.heap[swap]) {
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swap = leftIdx;
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}
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if (rightIdx < length && this.heap[rightIdx] > this.heap[swap]) {
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swap = rightIdx;
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}
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if (swap === idx) break;
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this.heap[idx] = this.heap[swap];
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this.heap[swap] = val;
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idx = swap;
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}
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}
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bubbleUp(): void {
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let idx = this.heap.length - 1;
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const val = this.heap[idx];
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while (idx > 0) {
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const parentIdx = Math.floor((idx - 1) / 2);
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const parent = this.heap[parentIdx];
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if (val <= parent) break;
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this.heap[parentIdx] = val;
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this.heap[idx] = parent;
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idx = parentIdx;
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}
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}
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}

‎insert-interval/Jeehay28.ts

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// TC: O(n)
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// SC: O(n)
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function insert(intervals: number[][], newInterval: number[]): number[][] {
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const result: number[][] = [];
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const n = intervals.length;
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let i = 0;
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// Add all intervals that come before newInterval
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while (i < n && intervals[i][1] < newInterval[0]) {
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result.push(intervals[i]);
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i++;
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}
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// Merge all overlapping intervals with newInterval
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while (i < n && intervals[i][0] <= newInterval[1]) {
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newInterval[0] = Math.min(intervals[i][0], newInterval[0]);
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newInterval[1] = Math.max(intervals[i][1], newInterval[1]);
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i++;
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}
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result.push(newInterval);
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// Add remaining intervals after newInterval
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while (i < n) {
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result.push(intervals[i]);
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i++;
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}
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return result;
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}
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‎kth-smallest-element-in-a-bst/Jeehay28.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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// TC: O(n)
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// SC: O(n)
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function kthSmallest(root: TreeNode | null, k: number): number {
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const result: number[] = [];
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const dfs = (node: TreeNode | null) => {
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if (!node) return;
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dfs(node.left);
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result.push(node.val);
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dfs(node.right);
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};
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dfs(root);
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return result[k - 1];
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}

‎lowest-common-ancestor-of-a-binary-search-tree/Jeehay28.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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// TC: O(n)
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// SC: O(1)
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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 || !p || !q) return null;
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let node = root;
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while (node) {
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if (node.val < p.val && node.val < q.val) {
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node = node.right!;
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} else if (node.val > p.val && node.val > q.val) {
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node = node.left!;
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} else {
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return node;
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}
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}
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return null;
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}
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// TC: O(n)
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// SC: O(n)
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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 || !p || !q) return null;
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// if (p.val < root.val && q.val < root.val) {
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// return lowestCommonAncestor(root.left, p, q);
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// } else if (p.val > root.val && q.val > root.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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