解法一：
public class Solution {
public String reverseString(String s) {
StringBuilder sb = new StringBuilder(s);
sb = sb.reverse();
return sb.toString();
}
}
解法二：
public class Solution {
//递归做法
public String reverseString(String s) {
int length = s.length();
if (length <= 1) return s;
String leftStr = s.substring(0, length / 2);
String rightStr = s.substring(length / 2, length);
return reverseString(rightStr) + reverseString(leftStr);
}
}
解法三：
public class Solution {
public String reverseString(String s) {
char[] c = s.toCharArray();
for(int i = 0, j = c.length - 1; i < j; i++, j--){
//从首尾开始，交换
char t = c[i];
c[i] = c[j];
c[j] = t;
}
return new String(c);
}
}
