threecolorsflags.java

ThreeColorFlags问题最早由E.W.Dijkstra所提出

import java.io.*;   
  
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("输入三色旗顺序（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);           
    }   
}