Add dynamic programming version.

Author: trekhleb

src/algorithms/uncategorized/best-time-to-buy-sell-stocks/__tests__/dpBestTimeToBuySellStocks.test.js

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+importdpBestTimeToBuySellStocksfrom'../dpBestTimeToBuySellStocks';
+
+describe('dpBestTimeToBuySellStocks',()=>{
+it('should find the best time to buy and sell stocks',()=>{
+letvisit;
+
+expect(dpBestTimeToBuySellStocks([1,5])).toEqual(4);
+
+visit=jest.fn();
+expect(dpBestTimeToBuySellStocks([1],visit)).toEqual(0);
+expect(visit).toHaveBeenCalledTimes(1);
+
+visit=jest.fn();
+expect(dpBestTimeToBuySellStocks([1,5],visit)).toEqual(4);
+expect(visit).toHaveBeenCalledTimes(2);
+
+visit=jest.fn();
+expect(dpBestTimeToBuySellStocks([5,1],visit)).toEqual(0);
+expect(visit).toHaveBeenCalledTimes(2);
+
+visit=jest.fn();
+expect(dpBestTimeToBuySellStocks([1,5,10],visit)).toEqual(9);
+expect(visit).toHaveBeenCalledTimes(3);
+
+visit=jest.fn();
+expect(dpBestTimeToBuySellStocks([10,1,5,20,15,21],visit)).toEqual(25);
+expect(visit).toHaveBeenCalledTimes(6);
+
+visit=jest.fn();
+expect(dpBestTimeToBuySellStocks([7,1,5,3,6,4],visit)).toEqual(7);
+expect(visit).toHaveBeenCalledTimes(6);
+
+visit=jest.fn();
+expect(dpBestTimeToBuySellStocks([1,2,3,4,5],visit)).toEqual(4);
+expect(visit).toHaveBeenCalledTimes(5);
+
+visit=jest.fn();
+expect(dpBestTimeToBuySellStocks([7,6,4,3,1],visit)).toEqual(0);
+expect(visit).toHaveBeenCalledTimes(5);
+
+visit=jest.fn();
+expect(dpBestTimeToBuySellStocks(
+[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20],
+visit,
+)).toEqual(19);
+expect(visit).toHaveBeenCalledTimes(20);
+});
+});

src/algorithms/uncategorized/best-time-to-buy-sell-stocks/dpBestTimeToBuySellStocks.js

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+/**
+ * Finds the maximum profit from selling and buying the stocks.
+ * DYNAMIC PROGRAMMING APPROACH.
+ *
+ * @param{number[]} prices - Array of stock prices, i.e. [7, 6, 4, 3, 1]
+ * @param{function(): void} visit - Visiting callback to calculate the number of iterations.
+ * @return{number} - The maximum profit
+ */
+constdpBestTimeToBuySellStocks=(prices,visit=()=>{})=>{
+visit();
+letlastBuy=-prices[0];
+letlastSold=0;
+
+for(letday=1;day<prices.length;day+=1){
+visit();
+constcurBuy=Math.max(lastBuy,lastSold-prices[day]);
+constcurSold=Math.max(lastSold,lastBuy+prices[day]);
+lastBuy=curBuy;
+lastSold=curSold;
+}
+
+returnlastSold;
+};
+
+exportdefaultdpBestTimeToBuySellStocks;