Java String 小练习

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
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
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

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。