编写一个函数，其作用是将输入的字符串反转过来。(反转字符串)

示例 1:

• 输入: “hello”
• 输出: “olleh”

示例 2:

• 输入: “A man, a plan, a canal: Panama”
• 输出: “amanaP :lanac a ,nalp a ,nam A”

F1:

 public String reverseString(String s) {
        char[] chars = s.toCharArray();
        StringBuilder sb = new StringBuilder();
        for (int i = chars.length - 1; i >= 0; i--) {
            sb.append(chars[i]);
        }
        return sb.toString();
    }

F2:  
public String reverseString2(String s) {
        return new StringBuilder(s).reverse().toString();
    }

F3: 
 public String reverseString3(String s) {
        char[] chars = s.toCharArray();
        char temp;
        int length = chars.length;
        for (int i = 0 ,j = length -1; i < length / 2 ; i++,j--) {
            temp = chars[i];
            chars[i] = chars[j];
            chars[j] = temp;
        }
        return new String(chars);
    }