如何使循环购买最大金额？

Question

我试图让我的代码购买最大数量的手机和配件。一部手机的价格是99.99美元，而一部配件的价格是9.99美元。我的银行账户上有1000个。如何使我的代码购买最大金额？我的代码目前购买9部手机和9部配件。它应该买9部手机和10个配件，而不是9部。

​

const ACCESSORY = 9.99;
const PHONE = 99.99;

var balance = 1000;
var total = 0;

var phones_total = 0;
var accessories_total = 0;

while (((total + PHONE) || (total + ACCESSORY)) < balance) {
  total = total + PHONE;
  phones_total = phones_total + 1;
    if ((total + ACCESSORY) < balance) {
      total = total + ACCESSORY;
      accessories_total = accessories_total + 1;
    }
}

console.log("total = " + total);
console.log("phones = " + phones_total);
console.log("accessories = " + accessories_total);

​

Answer 1

这句话是错的：

while (((total + PHONE) || (total + ACCESSORY)) < balance) {

这并不能测试这两种和是否小于balance。(total + PHONE) || (total + ACCESSORY)的值始终是total + PHONE，除非是0，否则就是total + ACCESSORY。由于total + PHONE从来不是0，这实际上相当于：

while ((total + PHONE) < balance) {

而且它从来没有测试是否有可用的余额只是一个附件。进行此测试的正确方法是：

while ((total + PHONE) < balance || (total + ACCESSORY) < balance) {

您还应该使用<=而不是<，以便能够准确地使用所有的钱。

但是在循环中，您仍然将PHONE添加到total中，即使只剩下足够的余额作为附件。你得先检查一下。

​

const ACCESSORY = 9.99;
const PHONE = 99.99;

var balance = 1000;
var total = 0;

var phones_total = 0;
var accessories_total = 0;

while ((total + PHONE) <= balance || (total + ACCESSORY) <= balance) {
   if ((total + PHONE) <= balance) {
     total = total + PHONE;
     phones_total = phones_total + 1;
   }
   if ((total + ACCESSORY) <= balance) {
     total = total + ACCESSORY;
     accessories_total = accessories_total + 1;
   }
 }

console.log(phones_total, accessories_total);

​

一种更简单的方法是用算术代替循环。除以手机+配件的成本，找出你能负担得起的配对数量。然后找出你还能买多少配件，然后再用剩下的东西买。

​

const ACCESSORY = 9.99;
const PHONE = 99.99;

var balance = 1000;

var phones_total = Math.floor(balance/(PHONE + ACCESSORY));
var remainder = balance - phones_total*(PHONE+ACCESSORY)
var accessories_total = phones_total + Math.floor(remainder/ACCESSORY);

console.log(phones_total, accessories_total);

​

Answer 2

给你：

const ACCESSORY = 9.99;
const PHONE = 99.99;

var balance = 1000;
var total = 0;

var phones_total = 0;
var accessories_total = 0;

while (((total + PHONE) < balance) || ((total + ACCESSORY) < balance)) {
    if((total + PHONE) < balance){
        total = total + PHONE;
        phones_total = phones_total + 1;
    }
    if ((total + ACCESSORY) < balance) {
        total = total + ACCESSORY;
        accessories_total = accessories_total + 1;
    }
}

console.log("total = " + total);
console.log("phones = " + phones_total);
console.log("accessories = " + accessories_total);

但有了这个平衡，你只能买9部手机和10部备用手机。

Answer 3

在循环条件下，您只需检查是否有剩余的钱作为附件。如果你不这样做，就没有必要处决身体了。

while ((total + ACCESSORY) <= balance) {
    if ( (total + PHONE) <= balance) {
        ++ phones_total;
        total = (phones_total * PHONE) + (accessories_total * ACCESSORY);
    }

    if ( (total + ACCESSORY) <= balance) {
        ++ accessories_total;
        total = (phones_total * PHONE) + (accessories_total * ACCESSORY);
    }
}

在身体上，首先检查是否有钱买一部手机，如果是这样更新总数，然后看看你是否还有钱买一个配件。

使用浮点数，一次又一次地添加它们会导致更多的累积错误，而不是像上面那样简单地计算total。