Python 未超索引情况下 显示 IndexError

Question

如下，我正在解 leetcode 第14题 找数组的最长公共前缀。

想法是先排序，找出最短的值，
然后循环最短值的长度次，然后再循环数组，对比最短值的索引和数组内其他值的索引是否相同.
不同就跳出循环返回最长公共前缀
不懂的是这里为什么会在未超索引的情况下显示 超索引呢？

代码如下

class Solution(object):
    def longestCommonPrefix(self, strs):
        strs.sort(key = len)
        if len(strs) >= 2:
            z = strs[0]
            for i in range(len(z)):
                for s in strs[1:]:
                    if z[i] != s[i]:
                        z = z[0:i]
                        break
                    else:
                        print(z[i], s[i], s, i, z)
            return z if z else ''
        elif len(strs) == 1:
            return strs[0]
        else:
            return ''

s = Solution()
print(s.longestCommonPrefix(["flower","flow","flight"]))

报错如下：

f f flower 0 flow
f f flight 0 flow
l l flower 1 flow
l l flight 1 flow
o o flower 2 flow
Traceback (most recent call last):
  File "C:\Users\Administrator\Downloads\shaoq.py", line 50, in <module>
    print(s.longestCommonPrefix(["flower","flow","flight"]))
  File "C:\Users\Administrator\Downloads\shaoq.py", line 38, in longestCommonPrefix
    if z[i] != s[i]:
IndexError: string index out of range
[Finished in 1.1s]

但是同样的循环我测试了下在 powershell 里面是可以运行的，奇怪

>>> x = ["flower","flow","flight"]
>>> x.sort(key = len)
>>> x
['flow', 'flower', 'flight']
>>> z = x[0]
>>> for i in range(len(z)):
...     for st in x[1:]:
...             print(z[i], st[i])
...
f f
f f
l l
l l
o o
o i
w w
w g
>>> for i in range(len(z)):
...     for st in x[1:]:
...             if z[i] != st[i]:
...                     print(i, z[i], st[i], z[0:i])
...
2 o i fl
3 w g flo

等解答，谢谢~

Answer 1

你在 powershell 里没有 z = z[0:i] 啊 ....

z = z[0:i] 之后，z 变短了，然后 i 还在继续增加，增加到 z 原来的长度

要测试的话，就用原样的程序来测试。