【剑指offer】面试题58（1）：翻转单词顺序

怼烎@ 2022-06-11 09:19 163阅读 0赞

## 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);
        }
    }