IndexError：数组反转中列表索引超出范围

Posted 2021-05-02

我正在尝试按组反转数组。我已经浪费了半个多小时来查找问题，但无法弄清楚索引超出范围的情况。这是我的代码：

def rev(A,S,N):
    start=S
    end=N

    while start<end:
        A[start],A[end]=A[end],A[start]   #error here
        start+=1
        end-=1
    return A


def reverseInGroups(A,N,K):
    #Your code here
    rev(A,0,K)
    rev(A,K,N)    #error here
    return A

这是我得到的错误

答案

根本不需要使用/迭代位置：

def rev(data, start, end):
    """Reverses the range start:end (end exclusive) of the given list. No safeguards whatsoever
    so only use with correct data. Out of bounds is irrelevant due to slices used to revers."""
    data[start:end] = data[start:end][::-1]  # you need end+1 if you want inclusive
    return data

def reverseInGroups(A,N,K):
    #Your code here
    rev(A,0,K)
    rev(A,K,N)    #error here
    return A


l = list(range(11))

print ( reverseInGroups(l , 8, 3)) # why N (the bigger number) first?

获取

2, 1, 0, 7, 6, 5, 4, 3, 8, 9, 10]
#0  1  2  3  4  5  6  7  8  9  10   # position in the list that got reversed: 3-7 

另一答案

怎么样

def rev(a,start,end, middle):
    assert 0 <= start <= middle <= end < len(a)
    a[start:middle] = reversed(a[start:middle])
    a[middle:end] = reversed(a[middle:end])
    return a