260th Commit

README.md

@@ -295,9 +295,10 @@ Problems:
 | Monotonic Stack         |                 |        |      |
 | ----------------------- | --------------- | ------ | ---- |
 | 739. Daily Temperatures | [Solution][739] | Medium | 詳解 |
-| 901. Online Stock Span  | Solution        | Medium | 詳解 |
+| 901. Online Stock Span  | [Solution][901] | Medium | 詳解 |
 
 [739]: ./src/page-7/739.%20Daily%20Temperatures/dailyTemperatures.ts
+[901]: ./src/page-9/901.%20Online%20Stock%20Span/StockSpanner.ts
 
 ## Advanced - Top Interview 150
 

src/page-9/901. Online Stock Span/README.md

@@ -0,0 +1,13 @@
+# 72. 股票價格跨距 (Online Stock Span)
+
+設計一個演算法，收集某些股票的每日報價並返回該股票當日價格的**跨距**。
+
+當日股票價格的**跨距**是指股票價格小於或等於當日價格的最大連續天數（從該日開始往回算）。
+
+- 例如，如果最近四天股票的價格是 `[7,2,1,2]`，今天股票的價格是 `2`，那麼今天的跨距是 `4`，因為從今天開始，股票的價格連續 `4` 天小於或等於 `2`。
+- 另外，如果最近四天股票的價格是 `[7,34,1,2]`，今天股票的價格是 `8`，那麼今天的跨距是 `3`，因為從今天開始，股票的價格連續 `3` 天小於或等於 `8`。
+
+實作 `StockSpanner` 類別：
+
+- `StockSpanner()` 初始化類別的物件。
+- `next(price: number): number` 給出今天的股價 `price`，返回該股票價格的**跨距**。

src/page-9/901. Online Stock Span/StockSpanner.test.ts

@@ -0,0 +1,14 @@
+import { StockSpanner } from './StockSpanner';
+
+describe('901. Online Stock Span', () => {
+  test('StockSpanner', () => {
+    const stockSpanner = new StockSpanner();
+    expect(stockSpanner.next(100)).toBe(1);
+    expect(stockSpanner.next(80)).toBe(1);
+    expect(stockSpanner.next(60)).toBe(1);
+    expect(stockSpanner.next(70)).toBe(2);
+    expect(stockSpanner.next(60)).toBe(1);
+    expect(stockSpanner.next(75)).toBe(4);
+    expect(stockSpanner.next(85)).toBe(6);
+  });
+});

src/page-9/901. Online Stock Span/StockSpanner.ts

@@ -0,0 +1,26 @@
+/**
+ * Accepted
+ */
+export class StockSpanner {
+  private stack: [number, number][];
+
+  constructor() {
+    // Initialize the stack, where each element is [price, span]
+    this.stack = [];
+  }
+
+  next(price: number): number {
+    let span = 1;
+
+    // While stack is not empty and the current price is greater than or equal to the price on top of the stack
+    while (this.stack.length > 0 && this.stack[this.stack.length - 1][0] <= price) {
+      // Pop the top of the stack and add its span to the current span
+      span += (this.stack.pop() as [number, number])[1];
+    }
+
+    // Push the current price and its span onto the stack
+    this.stack.push([price, span]);
+
+    return span;
+  }
+}