• [package Com.Xu.String;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

public class Six {
public static String convert(String s, int numRows) {
if(numRows1){
return s;
}
List rows=new ArrayList<>();
for(int i=0;i< Math.min(numRows,s.length());i++){
rows.add(new StringBuilder());
}
int curRow=0;
boolean goingDown=false;
for(Character c:s.toCharArray()){
rows.get(curRow).append(c);
if(curRow0||curRow==numRows-1){
goingDown=!goingDown;
}
curRow+=goingDown?1:-1;
}
StringBuilder ret=new StringBuilder();
for(StringBuilder row:rows){
ret.append(row);
}
return ret.toString();
}

public static void main(String[] args) {
    String s="ABCD";
    System.out.println(convert(s,3));
}

}
]