字符串挪移

import java.util.*;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static char[] ret;
    public static int cur;
    public static void dfs(char[] strArray,boolean flag){
        if(strArray.length==1){
            ret[cur++]=strArray[0];
            return;
        }
        int n=strArray.length;
        char[] nextArray;
        if(flag){
            nextArray=new char[(n+1)/2];
        }else{
            nextArray=new char[(n)/2];
        }
        int p=0;
        boolean newFlag=false;
        //flag通过本次是否最后一个元素加入ret来判断
        if(flag){
            for(int i=0;i<n;i++){
                if(i%2==0){
                    nextArray[p++]=strArray[i];
                    if(i==n-1){
                        newFlag=false;
                    }
                }else{
                    ret[cur++]=strArray[i];
                    if(i==n-1){
                        newFlag=true;
                    }
                }
            }
        }else{
            for(int i=0;i<n;i++){
                if(i%2==1){
                    nextArray[p++]=strArray[i];
                    if(i==n-1){
                        newFlag=false;
                    }
                }else{
                    ret[cur++]=strArray[i];
                    if(i==n-1){
                        newFlag=true;
                    }
                }
            }
        }
        dfs(nextArray,newFlag);
    }
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String str=in.nextLine();
        int n=str.length();
        ret=new char[n];
        int cur=0;
        char[] strArray=str.toCharArray();
        dfs(strArray,true);
        System.out.println(new String(ret));
    }
}