TopCoder SRM 507 Division 2 - 500 point problem

CubeStickers.java

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

public class CubeStickers {
    public String isPossible(String[] sticker) {
        Set<String> uniqueStickers = new HashSet<String>();
        for (String s : sticker) uniqueStickers.add(s);
        if (uniqueStickers.size() >= 5) return "YES";
        else {
            Map<String, Integer> colorsMap = new HashMap<String, Integer>();
            for (String s : sticker) colorsMap.put(s,colorsMap.containsKey(s) ? colorsMap.get(s) + 1 : 1);

            int pairs = 0;
            int singles = 0;
            for (Map.Entry<String, Integer> entry : colorsMap.entrySet()) {
                if (entry.getValue() >= 2) pairs++;
                else singles++;
            }
            return pairs * 2 + singles >= 6 ? "YES" : "NO";
        }
    }

}