코딩테스트 연습 - 해시- 완주하지 못한 선수

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import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
 
class Solution {
    public String solution(String[] participant, String[] completion) {
        String answer = "";
 
        Map<Integer, Object> participantMap = new HashMap<Integer, Object>();
 
        List<String> list = new ArrayList<String>();
        
        for(int i = 0; i < participant.length; i++) {
            list.add(participant[i]);
        }
        
        int key = 0;
        
        for (int i = 0; i < completion.length; i++) {
            String str = completion[i];
            if (list.contains(str)) {
                list.remove(str);
            };
        }
        
        for(int i = 0; i < list.size(); i++) {
            participantMap.put(i, list.get(i));
        }
        
        
        if(list.size() > 1){
            for (int j = 0; j < participantMap.size(); j++) {
                answer += participantMap.get(j) + " ";
            }
        }else{
            answer += participantMap.get(0);
        }
        return answer;
    }
}