红、白、蓝三色棋

假设有一条绳子，上面有红、白、蓝三种颜色的旗子，起初绳子上的旗子颜色并没有顺序，您希望将之分类，
并排列为蓝、白、红的顺序，要如何移动次数才会最少，注意您只能在绳子上进行这个动作，而且一次只能调换两个旗子。


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class ThreeColorsFlags {
    private void swap(char[] flags, int x, int y) {
        char temp;
        temp = flags[x];
        flags[x] = flags[y];
        flags[y] = temp;
    }
   
    public String move(char[] flags) {
        int wFlag = 0;
        int bFlag = 0;
        int rFlag = flags.length - 1;
   
        while(wFlag <= rFlag) {
            if(flags[wFlag] == 'W') {
                wFlag++;
            }
            else if(flags[wFlag] == 'B') {
                swap(flags, bFlag, wFlag);
                bFlag++;
                wFlag++;
            }
            else {
                while(wFlag < rFlag && flags[rFlag] == 'R')
                    rFlag--;
                swap(flags, rFlag, wFlag);
                rFlag--;               
            }
        }
       
        return new String(flags);
    }
   
    public static void main(String[] args)throws IOException
    {       
        BufferedReader buf;
        buf = new BufferedReader(
                    new InputStreamReader(System.in));

        System.out.print("输入三色棋顺序（ex. RWBBWRWR）：");
        String flags = buf.readLine();
       
        ThreeColorsFlags threeColorsFlag = new ThreeColorsFlags();
        flags = threeColorsFlag.move(
                   flags.toUpperCase().toCharArray());
       
        System.out.println("移动顺序后：" + flags);       
    }
}