javascript - 频率计数器未定义/2 的幂不等于

Question

所以问题是 2 个数组:

[1,2,2,4];
[1,4,4,16];

检查第一个数组中的项目在第二个数组中是否有重复项。

const counterNumber = (arr1,arr2) => {
    if(arr1.length !== arr2.length) return false

    let counter1 = {}
    let counter2 = {}

    for (let val of arr1){
        counter1[val] = ( counter1[val] || 0 )+ 1
    }

    for (let val of arr2){
         counter2[val] = ( counter2[val] || 0 )+ 1
    }

    for(let key in counter1){
        if(!(key ** 2 in counter2)) return false     
        if(counter2[key ** 2] !== counter1[key]) return false
    }

    return true
}

现在可以工作了，但我不明白这一行

if(counter2[key ** 2] !== counter1[key]) return false

这怎么不返回 false？第一个数组有 1,2,2,4，第二个数组有 1,4,4,16。

对于第一个数组，将值存储在一个对象中后，该对象将具有键 1,2,3。在 for in 循环中

counter2[key **2] is  counter[1 ** 2] / counter[1]  // counter1[1] 
counter2[key ** 2] is counter[ 2 ** 2] / counter[4] // counter1[2]
counte2[key ** 3] is counter{ 3 ** 2] / counter[9]  // counter1[3]


these are not === so therefore it should return false but instead if i console.log it gives me undefined and the return true appears.

Answer 1

最后一个 for 循环之前

counter1 是

const counter1 = {
  1: 1,
  2: 2,
  4: 1
}

counter2 是

const counter2 = {
  1: 1,
  4: 2,
  16: 1
}

这是一个根据arr1中的值描述不同变量的表格

+----+----------------+---+---+---+
| #1 | value in arr1  | 1 | 2 | 4 |
+----+----------------+---+---+---+
| #2 | counter1 key   | 1 | 2 | 4 |
+----+----------------+---+---+---+
| #3 | counter2 key   | 1 | 4 |16 |
+----+----------------+---+---+---+
| #4 | counter1 value | 1 | 2 | 1 |
+----+----------------+---+---+---+
| #5 | counter2 value | 1 | 2 | 1 |
+----+----------------+---+---+---+

下面的行检查两个数组中值的频率。

if(counter2[key ** 2] !== counter1[key]) return false

如果您查看表格，它会比较第 4 行和第 5 行；

代码可以像这样重构得更清晰

const counterNumber = (arr1,arr2) => {
    if(arr1.length !== arr2.length) return false

    let counter1 = {}
    let counter2 = {}

    for (let val of arr1){
        counter1[val] = ( counter1[val] || 0 )+ 1
    }

    for (let val of arr2){
         counter2[val] = ( counter2[val] || 0 )+ 1
    }

    for(let key in counter1){
        if(!hasMatchingSquareNumber(key, counter2)) return false     
        if(!hasMatchingSquareNumberCount(key, counter1, counter2)) return false
    }

    return true
}

const hasMatchingSquareNumber = (value, counter2) => {
    const valueToSquare =  value ** 2;
    return valueToSquare in counter2; 
}

const hasMatchingSquareNumberCount = (value, counter1, counter2) =>  {
    const valueToSquare =  value ** 2;
    return counter2[valueToSquare] === counter1[value];
}