Description
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]
Solution
我还能说什么呢，超级简单题。
class Solution {
public String reverseStr(String s, int k) {
if (k < 2 || s == null || s.length() < 2) return s;
int n = s.length();
char[] chars = s.toCharArray();
int i = 0;
while (i < n) {
reverse(chars, i, Math.min(i + k - 1, n - 1));
i += 2 * k;
}
return new String(chars);
}
public void reverse(char[] chars, int start, int end) {
while (start < end) {
swap(chars, start++, end--);
}
}
public void swap(char[] chars, int i, int j) {
char tmp = chars[i];
chars[i] = chars[j];
chars[j] = tmp;
}
}
