Problem 1.2.7 Broken Necklace

출처: https://train.usaco.org/usacogate

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문제 설명

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 can include any of 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.

입력 양식

Line 1: N, the number of beads
Line 2: a string of N characters, each of which is r, b, or w

출력 양식

A single line containing the maximum of number of beads that can be collected from the supplied necklace.

입력 예

29 
wwwbbrwrbrbrrbrbrwrwwrbwrwrrb

출력 예

11

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문제 풀이 내용

목걸이는 원형으로 연결되어 있으므로, 시작과 끝부분을 서로 연결해서 2번의 배열 안에서만 세면 가능하다. 흰색은 어떤 색이든 연결이 되고, 빨간색과 파란색이 서로 달라지는데, 두번 바뀌기 전까지 배열을 세는 방법이다.

프로그램 내용

#define MAX_BEAD 350

    int Length = 0;
    string Beads;

        Length = Beads.length();

    int count = 0;
    int MAX = 0;
    char color;
    int flag=0;

    string ExtBeads = Beads + Beads;

    for(int idx=0; idx < Length; ++idx)
    {
        char current = ExtBeads[idx];

        if(current == 'w')
            flag = 0;
        else
            flag = 1;

        count =0;

        int idx2 = idx;
        while( flag <=2 )
        {
            while (idx2 < (Length + idx) && ( ExtBeads[idx2] == current || ExtBeads[idx2] == 'w'))
            {
                count++;
                idx2++;
            }
            flag++;
            current = ExtBeads[idx2];
        }

        if ( count > MAX ) MAX = count;
    }

 

Chapter 1. Getting started