leetcode-541-Reverse-String-II

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描述

Given a string and an integer k, you need to reverse the first k characters for every 2k characters counting from the start of the string. If there are less than k characters left, reverse all of them. If there are less than 2k but greater than or equal to k characters, then reverse the first k characters and left the other as original.

Example:

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Input: s = "abcdefg", k = 2
Output: "bacdfeg"

Restrictions:

  1. The string consists of lower English letters only.
  2. Length of the given string and k will in the range [1, 10000]

分析

题意是给定一个字符串，要求每 2k 的字符串，将前 k 位倒转，如果最后不足 k 位，将其全部倒转，如果最后大于 k 位，不足 2k 为，倒转 k 位。

一次遍历即可。

解决方案1(Java)

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class Solution {
    public String reverseStr(String s, int k) {
        char[] result = s.toCharArray();
        for (int i = 0; i < result.length; i += 2*k) {
            int left = i, right = Math.min(left+k-1, result.length-1);
            while (left < right) {
                char tmp = result[left];
                result[left++] = result[right];
                result[right--] = tmp;
            }
        }
        return new String(result);
    }
}

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