Java String 小练习

淡淡的烟草味﹌ 2022-06-07 04:22 163阅读 0赞

最近无聊在leetcode做了几道String的题，主要是String 反转，虽然用StringBuider 调用reverse就行了，还是自己实现了一下。  
题目一、反转字符串  
传送门：[这里][Link 1]  
Write a function that takes a string as input and returns the string reversed.  
Example:  
Given s = “hello”, return “olleh”.  
关键代码：

public String reverseString(String s) {
            char[] a = s.toCharArray();
            int len = a.length;
            for(int i=0;i<len/2;i++){
                char t =a[i];
                a[i]=a[len-1-i];
                a[len-1-i]=t;
            }
            return new String(a);
        }

题目二、反转字符串3  
传送门：[这里][Link 2]  
Given a string, you need to reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.

Example 1:  
Input: “Let’s take LeetCode contest”  
Output: “s’teL ekat edoCteeL tsetnoc”  
Note: In the string, each word is separated by single space and there will not be any extra space in the string.

代码：分割一下就行了，再按上面的办法反转

class Solution { 
        public String reverseWords(String s) {
            String[] arr =s.split(" ");
            StringBuilder sb = new StringBuilder();
            for(int i=0;i<arr.length;i++){
                if(i!=arr.length-1)
                  sb.append(reverse(arr[i])+" ");
                else{
                  sb.append(reverse(arr[i]));
                }              
            }
            return sb.toString();
        }
        public String reverse(String str){
            char[] a = str.toCharArray();
            for(int i=0;i<a.length/2;i++){
                char t =a[i];
                a[i]=a[a.length-i-1];
                a[a.length-i-1]=t;
            }
            return new String(a);
        }
    }

题目三、对换字符串中的元音字符  
Write a function that takes a string as input and reverse only the vowels of a string.

Example 1:  
Given s = “hello”, return “holle”.

Example 2:  
Given s = “leetcode”, return “leotcede”.

Note:  
The vowels does not include the letter “y”.  
题目传送门：[这里][Link 3]

class Solution { 
        public String reverseVowels(String str) {
            if(str==null||str.equals("")) return str;
            char[] a =str.toCharArray();
            int s=0;
            int e=a.length-1;
            boolean flag=true;
            while(flag){
                while(!find(a[s])) {
                    s++;
                    if(s>=e){
                        flag=false;
                        break;
                    }
                }
                while(!find(a[e])) {
                    e--;
                    if(s>=e){
                        flag=false;
                        break;
                    }
                }
                if(flag){
                    char t=a[s];
                    a[s]=a[e];
                    a[e]=t;
                    s++;
                    e--;
                    if(s>=e){
                        flag=false;
                        break;
                    }
                }
            }
            return new String(a);
        }
        public boolean find(char c){ //查找元音字符
            if(c=='a'||c=='i'||c=='o'||c=='u'||c=='e'||c=='A'||c=='I'||c=='O'||c=='U'||c=='E'){
                return true;
            }
            return false;
        }
    }

吐槽：它给的例子元音是小写的 ，只写了小写的，考虑不周吧。

[Link 1]: https://leetcode.com/problems/reverse-string/description/
[Link 2]: https://leetcode.com/problems/reverse-words-in-a-string-iii/description/
[Link 3]: https://leetcode.com/problems/reverse-vowels-of-a-string/description/