代码随想录算法训练营第八天 | 344.反转字符串、541. 反转字符串II、卡码网：54.替换数字

344.反转字符串

双指针相向swap

class Solution:
    def reverseString(self, s: List[str]) -> None:
        """
        Do not return anything, modify s in-place instead.
        """
        left, right = 0, len(s) - 1
        while left < right:
            s[left], s[right] = s[right],s[left]
            left += 1
            right -= 1

541. 反转字符串II

自己实现：

class Solution:
    def reverseStr(self, s: str, k: int) -> str:
        left, right = 0, 2 * k
        res = ''
        while right < len(s):
            mid = (left + right) // 2
            res = res + s[left: mid][::-1] + s[mid: right]
            left = right
            right += 2 * k
        right = len(s)
        if right - left <= k:
            res += s[left:][::-1]
        else:
            res += s[left: left + k][::-1] + s[left + k:]
        return res

利用切片性质(切片索引超限返回空)可以更优雅实现：

class Solution:
    def reverseStr(self, s: str, k: int) -> str:
        p = 0
        while p < len(s):
            s = s[:p] + s[p: p + k][::-1] + s[p + k:]
            p += 2*k
        return s

卡码网：54.替换数字

这题Python也没法原地，再用切片吧。

import sys

def substitution(s):
    p = 0
    while p < len(s):
        if ord(s[p]) - ord('0') <= 9 and ord(s[p]) - ord('0') >= 0:
            s = s[0: p] + 'number' + s[p + 1:]
            p += 5
        p += 1
    return s
    
if __name__ == '__main__':
    s = input()
    print(substitution(s))