What causes panic: runtime error: index out of range [4] with length 4 even though array is initialized as dynamic array

Question

我已经初始化了一个动态数组，但它显示索引超出范围。我也试过给定长度，但它也显示同样的错误。错误描述：恐慌：运行时错误：索引超出范围 [4]，长度为 4

package main
import "fmt"
func missingNumber(nums []int) int {
arrSum := 0
arrLen := len(nums) + 1
for i := 0; i < arrLen; i++ {
arrSum += nums[i]
}
numSum := arrLen * (arrLen + 1) / 2
missingNumber := numSum - arrSum
return missingNumber
}
func main() {
nums := []int{1, 3, 4, 5}
result := missingNumber(nums)
fmt.Println(result)
}

Answer 1

这是您程序中的更正，用于从自然数序列中找到一个缺失的数字。您正在索引数组 nums[len(nums) + 1] 超出数组的范围。如果允许，这应该访问随机内存并读取任何合法的垃圾值，您甚至不会知道如此难以发现的错误。好处是 Go 会检查你是否只访问数组中存在的元素，而不是超出数组的元素。 Read this in Go specs

package main

import "fmt"

func missingNumber(nums []int) int {
    arrSum := 0
    arrLen := len(nums)
    for i := 0; i < arrLen; i++ {
        arrSum += nums[i]
    }
    //let n be the total natural number: which will be provided plus 1 missing
    n := arrLen + 1
    numSum := n * (n + 1) / 2
    missingNumber := numSum - arrSum
    return missingNumber
}
func main() {
    nums := []int{1, 3, 4, 5}
    result := missingNumber(nums)
    fmt.Println(result)
}

或者你可以使用范围循环来保证安全 or _, i := range nums { ... :

package main

import "fmt"

func missingNumber(nums []int) int {
    arrSum := 0
    arrLen := len(nums)

    for _, i := range nums {
        arrSum += i
    }
    //let n be the total natural number; which will be provided plus 1 missing
    n := arrLen + 1
    numSum := n * (n + 1) / 2
    missingNumber := numSum - arrSum
    return missingNumber
}
func main() {
    nums := []int{1, 3, 4, 5}
    result := missingNumber(nums)
    fmt.Println(result)
}

Answer 2

您应该将 arrLen := len(nums) + 1 更改为 arrLen := len(nums)。

您的数组长度为 4。索引为 0,1,2,3。但是当你试图做 arrLen := len(nums) + 1 时。 arrlen 值现在是 5。但你只有 4 个元素。从你的循环中你试图获得一个不存在于数组中的元素。这会给你一个运行时错误，它会恐慌。

这个适合你：

package main
import "fmt"
func missingNumber(nums []int) int {
arrSum := 0
arrLen := len(nums)
for i := 0; i < arrLen; i++ {
arrSum += nums[i]
}
m := arrLen + 1
numSum := m * (m + 1) / 2
missingNumber := numSum - arrSum
return missingNumber
}
func main() {
nums := []int{1, 3, 4, 5}
result := missingNumber(nums)
fmt.Println(result)
}

What causes panic: runtime error: index out of range [4] with length 4 even though array is initialized as dynamic array

What causes panic: runtime error: index out of range [4] with length 4 even though array is initialized as dynamic array

arrays

indexing

go

panic