【剑指offer】面试题58（1）：翻转单词顺序

题目

牛客最近来了一个新员工Fish，每天早晨总是会拿着一本英文杂志，写些句子在本子上。
同事Cat对Fish写的内容颇感兴趣，有一天他向Fish借来翻看，但却读不懂它的意思。
例如，“student. a am I”。
后来才意识到，这家伙原来把句子单词的顺序翻转了，正确的句子应该是“I am a student.”。
Cat对一一的翻转这些单词顺序可不在行，你能帮助他么？

思路

先对整个句子翻转：
　“student. a am I” -> “I ma a .tneduts”
再对每个单词进行逐个翻转（标点符号和普通字母一样处理）：
　“I ma a .tneduts” - > “I am a student.”

代码

public class _58_01_ReverseWordsInSentence {    public String ReverseSentence(String str) {        if(str == null || str.trim().length() <= 1)            return str;        char[] sentence = str.toCharArray();        // 翻转整个句子         reverse(sentence, 0, sentence.length - 1);        int low = 0;        int high = 0;        // 翻转每个单词        while(low != sentence.length && high != sentence.length) {            // 找到第一个非空格字符            while(low != sentence.length && sentence[low] == ' ')                ++low;            if(low == sentence.length)                break;            // 找到low后面的第一个空格字符            high = low + 1;            while(high != sentence.length && sentence[high] != ' ')                ++high;            reverse(sentence, low, high - 1);            low = high + 1;        }        return new String(sentence);    }    private void reverse(char[] str, int startIndex, int endIndex) {        for(int low = startIndex, high = endIndex; low < high;                ++low, --high) {            char t = str[low];            str[low] = str[high];            str[high] = t;        }    }}

测试

public class _58_01_Test {    public static void main(String[] args) {        test1();        test2();        test3();    }    private static void test1() {        _58_01_ReverseWordsInSentence rwis = new _58_01_ReverseWordsInSentence();        String s = rwis.ReverseSentence("student. a am I");        MyTest.equal(s, "I am a student.");        s = rwis.ReverseSentence("hello, peyton lin.");        MyTest.equal(s, "lin. peyton hello,");        // 两个空格         s = rwis.ReverseSentence("hello  ");        MyTest.equal(s, "  hello");    }    private static void test2() {        _58_01_ReverseWordsInSentence rwis = new _58_01_ReverseWordsInSentence();        String s = rwis.ReverseSentence("a");        MyTest.equal(s, "a");        s = rwis.ReverseSentence("abc");        MyTest.equal(s, "abc");        s = rwis.ReverseSentence("");        MyTest.equal(s, "");    }    private static void test3() {        _58_01_ReverseWordsInSentence rwis = new _58_01_ReverseWordsInSentence();        String s = rwis.ReverseSentence(null);        System.out.println(s);    }}