maxProfit.js

class ProfitCalculator {
  
  constructor(prices) {
    this.prices = prices
  }

  // implementation 1 uses standard for-loop
  getMaxProfit() {
    let maxProfit = 0
    let minPrice = this.prices[0]
    for (let i = 0; i < this.prices.length; i++) {
      minPrice = Math.min(minPrice, this.prices[i])
      maxProfit = Math.max(maxProfit, (this.prices[i] - minPrice))
    }
    return maxProfit
  }
  
  // implementation 2 uses functional-style (no variables, no loops)
  getMaxProfitFunctional() {
    return this.prices.reduce((acc, curr) => ({
      minPrice: Math.min(acc.minPrice, curr),
      maxProfit: Math.max(acc.maxProfit, curr - Math.min(acc.minPrice, curr))
    }), {
      minPrice: this.prices[0],
      maxProfit: 0
    }).maxProfit
  }
}

const calc = new ProfitCalculator([
  0.5,
  50,
  25.3,
  100,
  101,
  1000,
  42
])

console.log(
  calc.getMaxProfit(),
  calc.getMaxProfitFunctional()
)