Best Time to Buy and Sell Stock with Transaction Fee LeetCode solution in JavaScript

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/**
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 * @param {number[]} prices
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 * @param {number} fee
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 * @return {number}
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 */
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var maxProfit = function (prices, fee) {
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  let purchase = -1 * prices[0]; //If we purchase on 0th day
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  let sell = 0; //If we sell on 0th day
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  let prevPurchase;
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  for (let i = 1; i < prices.length; i++) {
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    prevPurchase = purchase;
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    purchase = Math.max(purchase, sell - prices[i]); //If we purchase on ith day
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    sell = Math.max(sell, prevPurchase + prices[i] - fee); //If we sell on ith day
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  }
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  return sell; //If must return the best price whenever we sold stock because then only we can be at max profit.
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};