[プログラマー]完走できなかった選手

1.問題解きに悩む

2.方法1-hashMapを無効にする

import java.util.Arrays;

class Solution {
    public String solution(String[] participant, String[] completion) {
        Arrays.sort(participant);
        Arrays.sort(completion);
        int i;
        for(i = 0; i < completion.length; i++){
            if(!participant[i].equals(completion[i])){
                return participant[i];
            }
        }
        return participant[i];
    }
}

3.方法2-hashMapの使用

import java.util.HashMap;

class Solution {
    public String solution(String[] participant, String[] completion) {
        String result = "";
        HashMap<String, Integer> hashMap = new HashMap<>();
        for(String p : participant){
            hashMap.put(p, hashMap.getOrDefault(p, 0) + 1);
        }
        for(String c : completion){
            hashMap.put(c, hashMap.get(c) - 1);
        }
        for(String key : hashMap.keySet()){
            if(hashMap.get(key) != 0){
                result = key;
                break;
            }
        }
        return result;
    }
}

4.学んだこと

String[] arr1 = {"qwe", "asd", "zxc", "qwe"};
String[] arr2 = {"qwe", "asd", "zxc"};

Map<String, Integer> map = new HashMap<>();
for(String a : arr1) map.put(a, map.getOrDefault(a, 0) + 1);
System.out.println(map);
// {qwe=2, asd=1, zxc=1}