Main.java

import java.util.Set;
import java.util.HashSet;
import java.util.TreeSet;

public class Main {
  public String solve(String input) {
    String[] inputs = input.split(":");
    char c = inputs[1].charAt(0);
    Set<Character> set = new HashSet<>();
    for (char s: inputs[0].toCharArray()) {
      int i = s - '0';
      set.add(c);
      if ((c - 'A') % 8 == i % 8) {
        c--;
        if (c < 'A') {
          c = 'H';
        }
      }
      else if (c - 'A' + 1 == i) {
        c++;
        if (c > 'H') {
          c = 'A';
        }
      }
    }
    set.add(c);
    StringBuilder builder = new StringBuilder();
    for (char s: "ABCDEFGH".toCharArray()) {
      if (set.add(s)) {
        builder.append(s);
      }
    }
    String str = builder.toString();
    set = new TreeSet<>();
    for (char x: str.toCharArray()) {
      for (char s: inputs[0].toCharArray()) {
        int i = s - '0';
        if ((x - 'A') % 8 == i % 8) {
          x--;
          if (x < 'A') {
            x = 'H';
          }
        } else if (x - 'A' + 1 == i) {
          x++;
          if (x > 'H') {
            x = 'A';
          }
        }
      }
      set.add(x);
    }
    builder = new StringBuilder();
    for (char x: set) {
      builder.append(x);
    }
    return builder.toString();
  }
}