Reverse String II — LeetCode 541 Python Solution

The problem

Given a string s and an integer k, reverse the first k characters for every 2k characters counting from the start of the string. If there are fewer than k characters left, reverse all of them.

Example

Input

s = "abcdefg", k = 2

Output

"bacdfeg"

Python solution

class Solution:
    def reverseStr(self, s: str, k: int) -> str:
        cs = list(s)
        for i in range(0, len(cs), 2 * k):
            cs[i : i + k] = reversed(cs[i : i + k])
        return "".join(cs)

Complexity

Pattern: Two Pointers

Use the order already in the input to discard half the search space at every step. LeetCode 541. Reverse String II is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Two Pointers.

The two pointers guide has the Python template for the pattern and the 201 LeetCode problems that use it.

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