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Commit 1c1b244

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Add dynamic programming version.
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import dpBestTimeToBuySellStocks from '../dpBestTimeToBuySellStocks';
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describe('dpBestTimeToBuySellStocks', () => {
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it('should find the best time to buy and sell stocks', () => {
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let visit;
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expect(dpBestTimeToBuySellStocks([1, 5])).toEqual(4);
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visit = jest.fn();
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expect(dpBestTimeToBuySellStocks([1], visit)).toEqual(0);
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expect(visit).toHaveBeenCalledTimes(1);
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visit = jest.fn();
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expect(dpBestTimeToBuySellStocks([1, 5], visit)).toEqual(4);
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expect(visit).toHaveBeenCalledTimes(2);
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visit = jest.fn();
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expect(dpBestTimeToBuySellStocks([5, 1], visit)).toEqual(0);
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expect(visit).toHaveBeenCalledTimes(2);
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visit = jest.fn();
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expect(dpBestTimeToBuySellStocks([1, 5, 10], visit)).toEqual(9);
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expect(visit).toHaveBeenCalledTimes(3);
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visit = jest.fn();
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expect(dpBestTimeToBuySellStocks([10, 1, 5, 20, 15, 21], visit)).toEqual(25);
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expect(visit).toHaveBeenCalledTimes(6);
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visit = jest.fn();
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expect(dpBestTimeToBuySellStocks([7, 1, 5, 3, 6, 4], visit)).toEqual(7);
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expect(visit).toHaveBeenCalledTimes(6);
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visit = jest.fn();
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expect(dpBestTimeToBuySellStocks([1, 2, 3, 4, 5], visit)).toEqual(4);
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expect(visit).toHaveBeenCalledTimes(5);
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visit = jest.fn();
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expect(dpBestTimeToBuySellStocks([7, 6, 4, 3, 1], visit)).toEqual(0);
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expect(visit).toHaveBeenCalledTimes(5);
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visit = jest.fn();
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expect(dpBestTimeToBuySellStocks(
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[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20],
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visit,
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)).toEqual(19);
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expect(visit).toHaveBeenCalledTimes(20);
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});
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});
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/**
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* Finds the maximum profit from selling and buying the stocks.
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* DYNAMIC PROGRAMMING APPROACH.
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*
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* @param {number[]} prices - Array of stock prices, i.e. [7, 6, 4, 3, 1]
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* @param {function(): void} visit - Visiting callback to calculate the number of iterations.
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* @return {number} - The maximum profit
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*/
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const dpBestTimeToBuySellStocks = (prices, visit = () => {}) => {
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visit();
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let lastBuy = -prices[0];
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let lastSold = 0;
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for (let day = 1; day < prices.length; day += 1) {
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visit();
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const curBuy = Math.max(lastBuy, lastSold - prices[day]);
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const curSold = Math.max(lastSold, lastBuy + prices[day]);
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lastBuy = curBuy;
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lastSold = curSold;
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}
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return lastSold;
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};
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export default dpBestTimeToBuySellStocks;

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