交换数组中的元素导致问题-解网

问：

新年快乐。我有一个关于在 Python 环境下交换数组中元素的问题。没有问题的代码是：

def findMissingNumber(nums):
    length = len(nums)
    result = []
    i = 0
    while i < length:
        # num = nums[i]
        target = nums[i] - 1
        if nums[i] != i+1 and nums[i] != nums[target]:
            # swap with the nums[i]-1
            nums[target], nums[i]= nums[i], nums[target]
        else:
            i += 1
    for j in range(length):
        if nums[j] != j+1:
            result.append(j+1)
    return result

print(findMissingNumber([2, 3, 1, 8, 2, 3, 5, 1]))
print(findMissingNumber([2, 4, 1, 2]))
print(findMissingNumber([2, 3, 2, 1]))

回答：

[4, 6, 7]
[3]
[4]

错误的是：

def findMissingNumber(nums):
    length = len(nums)
    result = []
    i = 0
    while i < length:
        num = nums[i]
        target = num - 1
        if num != i+1 and num != nums[target]:
            # swap with the num-1
            nums[target], num = num, nums[target]
        else:
            i += 1
    for j in range(length):
        if nums[j] != j+1:
            result.append(j+1)
    return result

print(findMissingNumber([2, 3, 1, 8, 2, 3, 5, 1]))
print(findMissingNumber([2, 4, 1, 2]))
print(findMissingNumber([2, 3, 2, 1]))

回答：

[4, 6, 7]
[3, 4]
[3, 4]

我不确定为什么引用（我应该这样称呼）会引起麻烦。你介意详细解释一下吗？
谢谢。

python 复制和交换

def findMissingNumber(nums):
    length = len(nums)
    result = []
    i = 0
    while i < length:
        # num and nums[i] have the same value but doesnt refer to same memory location
        num = nums[i]
        target = num - 1
        if num != i+1 and num != nums[target]:
            # swap with the num-1
            
            # incorrect swap, num value is not referencing the list index, but has a copy of its value,
            # so instead of swapping value with num, do it from the list like below
            # nums[target], num = num, nums[target]
            
            
            # correct swap
            nums[target], nums[i] = nums[i], nums[target]
        else:
            i += 1
    for j in range(length):
        if nums[j] != j+1:
            result.append(j+1)
    return result

print(findMissingNumber([2, 3, 1, 8, 2, 3, 5, 1]))
print(findMissingNumber([2, 4, 1, 2]))
print(findMissingNumber([2, 3, 2, 1]))

感谢您的帮助。我试着总结一下你分享的结果。如果为新变量赋值，例如 a = b[0]。a 是内存中的新位置，因此对 a 的任何更改都不会影响 b[0]。但是，如果为整个变量分配一个新的引用，比如 a = b，则 a 仍然指向内存中 b 的位置，b 的任何变化都会影响 b。请问为什么？欣赏。

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交换数组中的元素导致问题

swap elements in an array causing issue

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