JavaScript Fun Question: Buying a Car

Xiao Wang has a very old car, worth about 2,000 yuan, and it is easy to sell.

He took a fancy to a second-hand car worth 8,000 yuan and wanted to buy it after saving enough money.

He estimates that he can save 1,000 yuan every month.

The price of his current car and that second-hand car will be reduced every month, initially by 1%, and then every two months, the price reduction will increase by 0.5%.

For example, the price will be reduced by 1% in the first month, 1.5% in the second month, 1.5% in the third month, and 2% in the fourth month.

In other words, the price reduction in single months is the same as the previous month, and the price reduction in double months is 0.5% higher than the previous month.

Can you help him?

How many months of savings does he have to save to buy this used car? How much money will he have left after buying the car?

The function prototype is as follows:

nbMonths(startPriceOld, startPriceNew, savingperMonth, percentLossByMonth)

respectively corresponds to: old car price, second-hand car price, monthly deposit quota , the first month's decrease

Example:

nbMonths(12000, 8000, 1000, 1.5) // [0, 4000]

In this case, the old car is worth more than the second-hand car, so why wait? Just buy it! You can also earn 4,000 yuan!

nbMonths(8000, 8000, 1000, 1.5) // [0, 0]

In this case, just trade in the old one for the new one, and the two will be offset.

nbMonths(2000, 8000, 1000, 1.5) // [6, 766]

In this case, it will take 6 months, and the final balance is 766.158... wait for a series of decimals, and round up to 766 yuan.

This question is very simple addition, subtraction, multiplication and division, but don’t think too much about it, such as the idea of ​​depositing money in the bank to earn interest~

Okay, let’s go straight to the code:

function nbMonths(startPriceOld, startPriceNew, savingperMonth, percentLossByMonth){  
    percentLossByMonth /= 100;  
    var months = 1;  
    var percentLossIncrement = 0.005;  
    var alreadyHaveMoney = 0;  
    while(startPriceOld + alreadyHaveMoney < startPriceNew){  
        if(months % 2 === 0){  
            percentLossByMonth += percentLossIncrement;  
        }  
        startPriceOld *= (1 - percentLossByMonth);  
        startPriceNew *= (1 - percentLossByMonth);  
        alreadyHaveMoney += savingperMonth;  
        months++;  
    }  
    return [months-1,Math.round(startPriceOld + alreadyHaveMoney - startPriceNew)];  
}

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