TIRA 1.5 munkoodi

import java.util.*;

public class Main {
    public static int getDoublePosStart(StringBuilder sb, int start, int startlen) {
        for (; start < startlen; ++start) {
            if (sb.charAt(start) == sb.charAt(start - 1)) {
                return start;
            }
        }
        return -1;
    }

    public static int getDoublePosEnd(StringBuilder sb, int limit) {
        // for (int i = sb.length() - 1; i > limit; --i) {
        int i = sb.length() - 1;
        if (i > limit) {
            if (sb.charAt(i) == sb.charAt(i - 1)) {
                return i;
            }
        }
        return -1;
    }

    public static int getNonDoublePos(StringBuilder sb, char c, int oldpos) {
        for (int i = oldpos; i > 0; --i) {
            if (sb.charAt(i) != c && sb.charAt(i - 1) != c) {
                return i;
            }
        }
        return 0;
    }

    public static String xjarjestaMerkit(String mjono) {
        int amin = 255;
        int amax = 0;
        int[] amounts = new int[256];
        for (int i = 0; i < mjono.length(); ++i) {
            char c = mjono.charAt(i);
            ++amounts[c];
            amin = Math.min(amin, c);
            amax = Math.max(amax, c);
        }

        int[] firstcharloc = new int[256];

        boolean first = true;
        StringBuilder result = new StringBuilder();
        int lastpos = 1;
        for (char i = (char)amin; i <= amax; ++i) {
            if (amounts[i] <= 0) {
                continue;
            }

            // optimizaion for first
            if (first) {
                for (int j = 0; j < amounts[i]; ++j) {
                    result.append(i);
                }
                first = false;
                continue;
            }

            int startlen = result.length();
            for (int j = 0; j < amounts[i]; ++j) {
                int samepos = getDoublePosStart(result, lastpos, startlen);

                if (samepos >= 0) {
                    result.insert(samepos, i);
                    lastpos = samepos + 1;
                    ++startlen;
                } else {
                    firstcharloc[i]++;
                    result.append(i);
                    if (i == amax) {
                        int strend = result.length()-firstcharloc[i];
                        ++j;
                        for (; j < amounts[i]; ++j) {
                            int pos2 = getNonDoublePos(result, i, strend);
                            result.insert(pos2, i);
                            lastpos++;
                            strend = pos2;
                        }
                        break;
                    }
                }
            }
        }

        char oldchar = result.charAt(result.length() - 1);
        int oldpos = result.length() - firstcharloc[oldchar];
        while (true) {
            int pos = getDoublePosEnd(result, lastpos);
            if (pos < 0) {
                break;
            } else {
                char c = result.charAt(pos);
                if (c != oldchar) {
                    oldpos = result.length() - firstcharloc[c];
                }
                int pos2 = getNonDoublePos(result, c, oldpos);
                result.deleteCharAt(pos);
                result.insert(pos2, c);
                lastpos++;
            }
        }
        return result.toString();
    }



    static int amin = 255;
    static int amax = 0;
    static int total = 0;
    static int[] amounts = new int[256];

    public static char getNextChar(char lastChar)
    {
        char next = 255;
        for (char i = (char)amin; i <= amax && total > 0; ++i) {
            if (amounts[i] <= 0) {
                continue;
            }
            if (i == lastChar) {
                continue;
            }
            if (amounts[i] > total/2) {
                next = i;
                break;
            }
            next = (char)Math.min(next, i);
        }
        --amounts[next];
        --total;
        return next;
    }

    public static String jarjestaMerkit(String mjono) {
        for (int i = 0; i < mjono.length(); ++i) {
            char c = mjono.charAt(i);
            ++amounts[c];
            ++total;
            amin = Math.min(amin, c);
            amax = Math.max(amax, c);
        }

        StringBuilder sb = new StringBuilder();
        char c = 0;
        while (total > 0)
        {
            c = getNextChar(c);
            sb.append(c);
        }

        return sb.toString();
    }

    public static void main(String[] args) {
        if (true) {
            suuri3();
            return;
        }
        System.out.println(jarjestaMerkit("AAABBB"));
        System.out.println(jarjestaMerkit("AAABBBCCCCCCCDDDDD"));
        System.out.println(jarjestaMerkit("BAAACCC"));
        System.out.println(jarjestaMerkit("CBAED"));
        System.out.println(jarjestaMerkit("AXAXA"));
    }

    public static void suuriTesti(String alku, String loppu) {
        String uusi = jarjestaMerkit(alku);
        System.out.println(uusi.equals(loppu));
        System.out.println(uusi);
        System.out.println(loppu);
        System.out.println(uusi.length());
        System.out.println(uusi.substring(uusi.length() - 200));
    }

    public static void suuri3() {
        int n = 99999;
        char[] t = new char[n];
        char[] u = new char[n];
        for (int i = 0; i < n; i++) {
            if (i % 2 == 0) {
                t[i] = 'X';
            } else if (i < n / 2) {
                t[i] = 'A';
            } else {
                t[i] = 'B';
            }
            u[i] = t[i];
        }
        Arrays.sort(u);
        suuriTesti(new String(u), new String(t));
    }
}