題目及測試用例

package pid344;
/*反轉字串

編寫一個函式，其作用是將輸入的字串反轉過來。

示例 1:

輸入: "hello"
輸出: "olleh"

示例 2:

輸入: "A man, a plan, a canal: Panama"
輸出: "amanaP :lanac a ,nalp a ,nam A"




*/


public class main {

    public static void main(String[] args) {
        String [] testTable = {"hello","A man, a plan, a canal: Panama"
 
,"av12,./34\\45"};
        for (String ito : testTable) {
            test(ito);
        }
    }

    private static void test(String ito) {
        Solution solution = new Solution();
        String rtn;
        long begin = System.currentTimeMillis();
        System.out.print(ito);          
        System.out
 
.println();
        //開始時列印陣列

        rtn= solution.reverseString(ito);//執行程式
        long end = System.currentTimeMillis();  

        System.out.println(":rtn" );
        System.out.print(rtn);
        System.out.println();
        System.out.println("耗時：" + (end - begin) + "ms");
        System.out.println("-------------------"
 
);
    }

}

解法1（成功，5ms，速度較慢）
建立一個stringbuilder，將string的順序 charAt(i) 插入stringbuilder，最後再轉為字串

package pid344;

import java.util.Arrays;

public class Solution {
public String reverseString(String s) {
        //相當於重寫stringbuilder的reverse方法
        StringBuilder build=new StringBuilder();
        int length=s.length();
        for(int i=0;i<length;i++){
            build.append(s.charAt(length-1-i));
        }        
    return build.toString();
    }



}

解法2（別人的，2ms，很快）
將字串化為char陣列，前後用temp顛倒

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