Incorrect Answer in Broken Necklace Problem USACO [closed]

Answer 1

Its an old thread, but might be useful to people learning programming. Here is a simple solution using brute force. The idea is that we make one pass through the data to count colours. In the second loop we perform pairwise comparison of sums from the left and the right part. Code should be easy to follow:

import java.io.*;
import java.util.LinkedList;
import java.util.List;
import java.util.TreeSet;

public class beads {

    public static void main(String[] args) throws IOException {
        BufferedReader f = new BufferedReader(new FileReader("beads.in"));
        PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("beads.out")));
        f.readLine();//length
        String s1 = f.readLine();
        List counts = new LinkedList();
        char[] colors = (s1.concat(s1)).toCharArray();
        char previousColor = ' ';
        int count = 0;
        for (char color : colors) {
            if (previousColor != color && count > 0) {
                counts.add(count + "-" + previousColor);
                count = 0;
            }
            count++;
            previousColor = color;
        }

        if (counts.isEmpty()) {//special case when there is only one color
            out.println(count/2);
            out.close();
            System.exit(0);
        }
        TreeSet result = new TreeSet();
        for (int i = 1; i < counts.size(); i++) {
            if(counts.get(i).split("-")[1].charAt(0)=='w')continue;
            int left = getLeft(counts, i);
            int right = getRight(counts, i);
            result.add((left+right));
        }
        out.println(result.last());
        out.close();
        System.exit(0);
    }

    private static int getLeft(List counts, int i) {
        char start = counts.get(i - 1).split("-")[1].charAt(0);
        boolean doContinue = true;
        int count = 0;
        while (doContinue) {
            String[] s = counts.get(--i).split("-");
            char color=s[1].charAt(0);
            if(start=='w' && color!='w')start=color;
            boolean incr = (color == 'w' || color==start);
            if(incr)
                count += Integer.parseInt(s[0]);
            else doContinue=false;

            doContinue = doContinue && i > 0;
        }
        return count;
    }


    private static int getRight(List counts, int i) {
        char start = counts.get(i).split("-")[1].charAt(0);
        boolean doContinue = true;
        int count = 0;
        while (doContinue) {
            String[] s = counts.get(i).split("-");
            char color=s[1].charAt(0);
            if(start=='w' && color!='w')start=color;

            boolean incr = (color == 'w' || color == start);
            if(incr)
                count += Integer.parseInt(s[0]);
            else doContinue=false;

            doContinue = doContinue && ++i < counts.size()-1;
        }
        return count;
    }
}