541. Reverse String II

原创于 2018-08-14 22:06:11 发布 · 86 阅读

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本文介绍了一种特殊的字符串反转算法，该算法每隔2k个字符反转前k个字符，特殊情况按特定规则处理。通过实例演示了输入abcdefg及k=2时的处理过程和输出结果。

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:

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

Restrictions:

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

程序如下所示：

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