用于二维数组的循环范围

Question

我正在参加 Advent Code Challenge，并且运行进入了大厅。我之前解决了这个错误，但在这种情况下，我被卡住了。下面的代码给了我一个 Uncaught TypeError: Cannot read properties of undefined. 相对于 switch (diagArray[i][j]).

我的想法是 diagArray 超出范围。是真的吗？

拜托，任何帮助都很棒！

const diagArray = [
  [0,1,0,0,0,1,1,1,0,0,0,1],
  [1,1,0,1,0,0,0,0,0,0,0,1],
  [1,1,1,0,0,1,0,0,1,0,1,1]
 ]; // example data
  
  for(let i = 0; i < diagArray.length; i++) {
  for (let j = 0; j < diagArray.length; i++) {
    let gammaRate = ''
    let epsilonRate = ''
    let ones = 0
    let zeros = 0
    let rates = []

    switch (diagArray[i][j]) {
      case 1:
        ones++
        break
      case 0:
        zeros++
        break
      default:
        break
    }

    if (ones > zeros) {
      gammaRate+=1
      epsilonRate+=0
    } else {
      gammaRate+=0
      epsilonRate+=1
    }

    rates.push([gammaRate, epsilonRate])
    // console.log(rates)
  }
}

Answer 1

这是因为在第二个 for 循环中它说 diagArray.length，它应该是 diagArray[i].length 这样你就得到了第二个数组的长度。

Answer 2

您的第二次迭代增加了 i 变量而不是 j，同时迭代到 diagArray 的长度而不是 diagArray[i]。

您可以使用控制台 API 调试您的值，无需猜测即可找出问题的根源。

const diagArray = [
  [0,1,0,0,0,1,1,1,0,0,0,1],
  [1,1,0,1,0,0,0,0,0,0,0,1],
  [1,1,1,0,0,1,0,0,1,0,1,1]
 ]; // example data
  
  for(let i = 0; i < diagArray.length; i++) {
  for (let j = 0; j < diagArray[i].length; j++) {
    let gammaRate = ''
    let epsilonRate = ''
    let ones = 0
    let zeros = 0
    let rates = []
    
    console.log(`${i}:${j} = ${diagArray[i][j]}`)

    switch (diagArray[i][j]) {
      case 1:
        ones++
        break
      case 0:
        zeros++
        break
      default:
        break
    }

    if (ones > zeros) {
      gammaRate+=1
      epsilonRate+=0
    } else {
      gammaRate+=0
      epsilonRate+=1
    }

    rates.push([gammaRate, epsilonRate])
    // console.log(rates)
  }
}

Answer 3

您应该像这样更新第二个 for 循环表达式。

for (let j = 0; j < diagArray[i].length; j++) {

Answer 4

for(let i = 0; i < diagArray.length; i++) {
  for (let j = 0; j < diagArray.length; i++) {

这里有多个问题。

第一个for循环没问题，但第二个for循环需要受限于内部数组的长度：

diagArray[i].length

而且它目前还在增加第一个循环计数i++。那需要 j++

工作示例：

const diagArray = [
  [0,1,0,0,0,1,1,1,0,0,0,1],
  [1,1,0,1,0,0,0,0,0,0,0,1],
  [1,1,1,0,0,1,0,0,1,0,1,1]
 ]; // example data
  
for (let i = 0; i < diagArray.length; i++) {
  for (let j = 0; j < diagArray[i].length; j++) {
    let gammaRate = ''
    let epsilonRate = ''
    let ones = 0
    let zeros = 0
    let rates = []

    switch (diagArray[i][j]) {
      case 1:
        ones++
        break
      case 0:
        zeros++
        break
      default:
        break
    }

    if (ones > zeros) {
      gammaRate+=1
      epsilonRate+=0
    } else {
      gammaRate+=0
      epsilonRate+=1
    }

    rates.push([gammaRate, epsilonRate])
    console.log(rates)
  }
}

另外，通常不建议使用这样的循环来迭代数组，因为正如您所发现的，很容易搞砸索引。

我建议改为对数组的值进行交互：

for (const row of diagArray) {
  for (const value of row) {

const diagArray = [
  [0,1,0,0,0,1,1,1,0,0,0,1],
  [1,1,0,1,0,0,0,0,0,0,0,1],
  [1,1,1,0,0,1,0,0,1,0,1,1]
 ]; // example data
  
for (const row of diagArray) {
  for (const value of row) {
    let gammaRate = ''
    let epsilonRate = ''
    let ones = 0
    let zeros = 0
    let rates = []

    switch (value) {
      case 1:
        ones++
        break
      case 0:
        zeros++
        break
      default:
        break
    }

    if (ones > zeros) {
      gammaRate+=1
      epsilonRate+=0
    } else {
      gammaRate+=0
      epsilonRate+=1
    }

    rates.push([gammaRate, epsilonRate])
    console.log(rates)
  }
}

用于二维数组的循环范围

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