回答編集履歴
2
Java8の書き方追加
answer
CHANGED
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@@ -19,4 +19,14 @@
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19
19
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= IntStream.rangeClosed('a', 'z')
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20
20
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.map(c -> Map.entry((char)c, (int)(Math.random() * MAX + 1))
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21
21
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.collect(groupingBy(e -> e.getValue(), mapping(e -> e.getKey(), toList())));
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22
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+
```
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23
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+
Java8ならこうなるか
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24
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+
```java
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25
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+
// import static java.util.stream.Collectors.*;
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26
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+
final int MAX = 10;
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27
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+
Map<Integer, List<Character>> map
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28
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+
= IntStream.rangeClosed('a', 'z')
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29
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.collect(toMap(c -> (char)c, c -> (int)(Math.random() * MAX + 1))
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30
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+
.entrySet().stream()
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31
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+
.collect(groupingBy(e -> e.getValue(), mapping(e -> e.getKey(), toList())));
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22
32
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```
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1
Streamでマッピング
answer
CHANGED
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@@ -1,3 +1,4 @@
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1
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+
computeIfAbsentとかgetOrDefaultとかを活用
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1
2
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```java
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2
3
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final int MAX = 10;
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3
4
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Random r = new Random();
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@@ -9,4 +10,13 @@
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9
10
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for (int i = 1; i <= MAX; i++) {
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10
11
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System.out.println(map.getOrDefault(Collections.emptyList()));
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11
12
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}
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13
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+
```
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14
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+
Java9以上ならStreamでこんな書き方もできるが、ここで使っているMap.entryじゃなくても2つの値をペアにしてオブジェクトを作れればなんでもいい
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15
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+
```java
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16
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+
// import static java.util.stream.Collectors.*;
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17
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+
final int MAX = 10;
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18
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+
Map<Integer, List<Character>> map
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19
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+
= IntStream.rangeClosed('a', 'z')
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20
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+
.map(c -> Map.entry((char)c, (int)(Math.random() * MAX + 1))
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21
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+
.collect(groupingBy(e -> e.getValue(), mapping(e -> e.getKey(), toList())));
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12
22
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```
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