Broken+Necklace

USACO 1.1 - Broken Necklace
You have a necklace of N red, white, or blue beads (3<=N<=350) some of which are red, others blue, and others white, arranged at random. Here are two examples for n=29:

1 2 1 2 r b b r b r r b r b b b r r b r r r w r b r w w b b r r b b b b b b r b r r b r b r r r b r r r r r r b r b r r r w Figure A Figure B r red bead b blue bead w white bead

The beads considered first and second in the text that follows have been marked in the picture.

The configuration in Figure A may be represented as a string of b's and r's, where b represents a blue bead and r represents a red one, as follows: brbrrrbbbrrrrrbrrbbrbbbbrrrrb.

Suppose you are to break the necklace at some point, lay it out straight, and then collect beads of the same color from one end until you reach a bead of a different color, and do the same for the other end (which might not be of the same color as the beads collected before this).

Determine the point where the necklace should be broken so that the most number of beads can be collected. Example

For example, for the necklace in Figure A, 8 beads can be collected, with the breaking point either between bead 9 and bead 10 or else between bead 24 and bead 25.

In some necklaces, white beads had been included as shown in Figure B above. When collecting beads, a white bead that is encountered may be treated as either red or blue and then painted with the desired color. The string that represents this configuration will include the three symbols r, b and w.

Write a program to determine the largest number of beads that can be collected from a supplied necklace. PROGRAM NAME: beads INPUT FORMAT Line 1: N, the number of beads Line 2: a string of N characters, each of which is r, b, or w SAMPLE INPUT (file beads.in)

29 wwwbbrwrbrbrrbrbrwrwwrbwrwrrb

OUTPUT FORMAT A single line containing the maximum of number of beads that can be collected from the supplied necklace. SAMPLE OUTPUT (file beads.out)

11

OUTPUT EXPLANATION Consider two copies of the beads (kind of like being able to runaround the ends). The string of 11 is marked.

wwwbbrwrbrbrrbrbrwrwwrbwrwrrb wwwbbrwrbrbrrbrbrwrwwrbwrwrrb

Source Code code format="java" /* ID: wjh3331 LANG: JAVA TASK: beads

import java.io.*;

public class beads { public static final int RED = 1; // 붉은 구슬 상태 public static final int BLUE = 2; // 푸른 구슬 상태

public static final int START = 4; // 시작 상태 public static final int STAGE1 = 8; // 시작상태에서 붉은 구슬이나 푸른 구슬을 만났을때의 상태 public static final int STAGE2 = 16; // 단계1 상태와 다른 색을 만났을때의 상태 public static final int END = 32; // 단계 2와 다른 색을 만났을때의 종료 상태

public static void main(String[] args) throws IOException { BufferedReader in = new BufferedReader(new FileReader("beads.in")); PrintWriter out = new PrintWriter(new FileWriter("beads.out"));

int n = Integer.parseInt(in.readLine); // 구슬의 개수 String necklace = in.readLine; // 목걸이 구슬들

int max = 0; // 주운 구슬의 최대 개수 for (int i = 0; i < n; i++) { int index = i; // 현재 판단하는 구슬의 위치 int count = 0; // 이을 수 있는 구슬의 개수 int state = START; // 시작 상태로 초기화 while (state != END) { char ch = necklace.charAt(index); // 구슬 하나를 선택

switch (state) { case START: // 시작 상태인데 if (ch == 'r') { // 붉은 색이라면 state = STAGE1 | RED; // 첫번째 붉은 구슬 단계로 } else if (ch == 'b') { // 푸른 색이라면 state = STAGE1 | BLUE; // 첫번째 푸른 구슬 단계로 }         count++;  // 개수 추가 index++; // 다음 위치로 break; case STAGE1 | RED: // 첫번째 붉은 구슬 단계에서 if (ch == 'b') { // 다른 색인 푸른 구슬이라면 state = STAGE2 | BLUE; // 두번째 푸른 구슬 단계로 }         count++; index++; break; case STAGE1 | BLUE: // 첫번째 푸른 구슬 단계에서 if (ch == 'r') { // 다른 색인 붉은 구슬이라면 state = STAGE2 | RED; // 두번째 붉은 구슬 단계로 }         count++; index++; break; case STAGE2 | RED: // 두번째 붉은 구슬 단계에서 if (ch == 'b') { // 다른 색인 푸른 구슬이라면 state = END; // 종료 상태로 break; }         count++; index++; break; case STAGE2 | BLUE: // 두번째 푸른 구슬 단계에서 if (ch == 'r') { // 다른 색인 붉은 구슬이라면 state = END; // 종료 상태로 break; }         count++; index++; break; default: break; }

// 최대값을 구한다. if (count > max) { max = count; }

// 끝까지 도착하면 앞으로 돌아간다. index %= n;       if(index == i) { break; }     }    }    out.println(max);  // 최대 개수를 출력한다.

// 종료한다. out.close; System.exit(0); } } code

Comment 갈수록 문제가 완전 어렵네요... 영어 실력이 부족함을 팍팍 느낍니다... 열공해야지... 유한상태머신으로 풀어보았습니다.