【剑指offer-Java版】42翻转单词顺序VS左旋转字符串

清疚 2022-08-21 10:45 136阅读 0赞

反转单词顺序以及左旋转字符串：输入一个英文句子，翻转句子中的单词顺序，单词内部的字母顺序是不变的 – I am a student. -> student. am I

第一步，翻转句子中的所有字符串，第二步翻转单词顺序

public class _Q42<T> {
        
    
        public char[] ReverseSentence(String str){
            if(str == null) return null;
            if(str.length() == 0) return str.toCharArray();
    
            char chars[] = str.toCharArray();
            reverse(chars, 0, str.length() - 1);
            int start = 0; 
            for(int i=0; i<str.length(); i++){
                if(chars[i] == ' '){
                    reverse(chars, start, i - 1);
                    start = i + 1;
                }
            }
            reverse(chars, start, str.length() - 1);
    
            return chars;
        }
    
        private void reverse(char chars[], int begin, int end){
            if(chars == null) return;
    
            if(begin == end) return;
    
            char c;
            while(begin < end){
                c = chars[begin];
                chars[begin] = chars[end];
                chars[end] = c;
                begin++;
                end--;
            }
        }
    
        public char[] LeftRotateString(String str, int n){
            if(str == null) return null;
    
            char chars[] = str.toCharArray();
            // 先分段旋转
            reverse(chars, 0 , n - 1);
            reverse(chars, n, str.length() - 1);
            // 最后整体旋转
            reverse(chars, 0, str.length() - 1);
    
            return chars;
        }
    
        }

测试代码：

public class _Q42Test extends TestCase {
        
    
        _Q42<?> reverse = new _Q42();
    
        public void test(){
            String str1 = "I am a student.";
    
            System.out.println(reverse.ReverseSentence(str1)); // 需要对返回结果进行非空判断
    
            String str2 = "abcdefg";
            int n = 2;
            System.out.println(reverse.LeftRotateString(str2, n)); // 
        }
        }