题解 | #反转字符串#

import java.util.*;


public class Solution {
    /**
     * 反转字符串
     * @param str string字符串 
     * @return string字符串
     */
  //时间复杂度O(n),空间复杂度O(n)
    public String solve (String str) {
        // write code here
        char[] c = new char[str.length()];
        int j=0;
        for(int i=str.length()-1;i>=0;i--){
            c[j] = str.charAt(i);
            j++;
        }
        return new String(c);    //字符转换为字符串
    }
}

//想要在原地交换，就要将字符串转换为字符数组
//时间复杂度O(n),空间复杂度O(1)
import java.util.*;
public class Solution {
    public String solve (String str) {
        char[] cstr = str.toCharArray();   
        int len = str.length();
        for(int i = 0 ; i < len/2 ;i++)
        {
                char t = cstr[i];
                cstr[i] = cstr[len-1-i];
                cstr[len-1-i]=t;
        }
        return new String(cstr);
    }
}