JZ44 翻转单词序列

https://www.nowcoder.com/practice/3194a4f4cf814f63919d0790578d51f3

第一次：

public class Solution {
    public String ReverseSentence(String str) {
        if (str.isEmpty()) return "";
        String[] arr = str.split(" ");
        // byte[] bytes = str.getBytes();
        // 双指针交换
        int low = 0;
        int high = arr.length - 1;
        while (high > low) {
            String tmp = arr[high];
            arr[high] = arr[low];
            arr[low] = tmp;
            low++;
            high--;
        }

        StringBuilder result = new StringBuilder();
        for (int i = 0; i < arr.length; i++) {
            if (i == arr.length - 1) {
                result.append(arr[i]);
            } else {
                result.append(arr[i]).append(" ");
            }
        }
        
        return result.toString();
    }
}

第二次

第一次做只想着快速刷完，完全不考虑实际面试不能使用字符串方法的问题，其实这题思路和上一题一样，都是旋转字符串，大致思路就是先旋转整个句子，然后各个单词逐个旋转

public class Solution {
    public String ReverseSentence(String str) {
        if (str.isEmpty()) return "";
        char[] strs = str.toCharArray();
        // 先整个翻转一遍
        reverse(strs, 0 , strs.length - 1);
        // 使用双指针计算一个单词的位置
        int low = 0;
        int high = 1;
        int len = strs.length;
        
        while (high < len) {
            boolean flag = high + 1 == len;
            if (strs[high] == ' ' || flag) {
                reverse(strs, low, flag ? high : high - 1);
                high++;
                low = high;
            } else {
                high++;
            }
        }
        
        return new String(strs);
    }
    
    // 翻转字符串
    private void reverse(char[] arr, int s, int e) {
        int left = s;
        int right = e;
        while (left < right) {
            char t = arr[left];
            arr[left] = arr[right];
            arr[right] = t;
            left++;
            right--;
        }
    }
}