Reverse Words in a String II

第一次写比较笨拙, 嵌套使用了stringbuilder, subsubstring和reverse

public class Solution {
    public String reverseStr(String s, int k) {
        StringBuilder sb = new StringBuilder(s);
        StringBuilder ans = new StringBuilder();
        while(sb.length()>2*k){
            ans.append(new StringBuilder(sb.substring(0,k)).reverse());
            ans.append(sb.substring(k,2*k));
            sb = new StringBuilder(sb.substring(2*k));
        }

        if(sb.length()<k){
            ans.append(sb.reverse());
        }
        else{
            ans.append(new StringBuilder(sb.substring(0,k)).reverse());
            ans.append(sb.substring(k));
        }
        return ans.toString();
    }
}

更简单的方式是写一个swap函数在原string上做操作. 参考论坛里的代码

public class Solution {
    public String reverseStr(String s, int k) {
        char[] arr = s.toCharArray();
        int n = arr.length;
        int i = 0;
        while(i < n) {
            int j = Math.min(i + k - 1, n - 1);
            swap(arr, i, j);
            i += 2 * k;
        }
        return String.valueOf(arr);
    }
    private void swap(char[] arr, int l, int r) {
        while (l < r) {
            char temp = arr[l];
            arr[l++] = arr[r];
            arr[r--] = temp;
        }
    }
}