feat: BridgesGeneratorByCreatingCandidates

모든 Line 후보를 만들어놓고 shuffle을 통해 하나의 후보를 꺼내쓰는 전략

Author: yumble

src/main/java/nextstep/ladder/model/BridgesGeneratorByCreatingCandidates.java

@@ -0,0 +1,49 @@
+package nextstep.ladder.model;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class BridgesGeneratorByCreatingCandidates implements BridgesGenerator {
+
+    private static List<List<Bridge>> candidates = new ArrayList<>();
+
+    static void generateLadders(int numbersOfPeople) {
+        List<List<Bridge>> result = new ArrayList<>(List.of(List.of(Bridge.of(false)), List.of(Bridge.of(true))));
+
+        for (int i = 2; i < numbersOfPeople ; i++) {
+            result = dp(result);
+        }
+
+        candidates = result;
+    }
+
+    static List<List<Bridge>> dp(List<List<Bridge>> result) {
+        return result.stream()
+                .flatMap(ladder -> {
+                    List<Bridge> withFalse = new ArrayList<>(ladder);
+                    withFalse.add(Bridge.of(false));
+                    List<Bridge> withTrue = new ArrayList<>(ladder);
+                    if (!ladder.get(ladder.size() - 1).canCrossBridge()) {
+                        withTrue.add(Bridge.of(true));
+                        return Stream.of(withFalse, withTrue);
+                    }
+                    return Stream.of(withFalse);
+                })
+                .collect(Collectors.toList());
+    }
+
+    @Override
+    public List<Bridge> generateBridges(Integer numbersOfPeople) {
+        if (candidates.isEmpty()) {
+            generateLadders(numbersOfPeople);
+        }
+        Collections.shuffle(candidates);
+        return candidates.get(0);
+    }
+
+
+
+}

src/main/java/nextstep/ladder/model/SequentialRandomBridgesGenerator.java src/main/java/nextstep/ladder/model/BridgesGeneratorBySequentialRandom.java

@@ -4,7 +4,7 @@
 import java.util.List;
 import java.util.concurrent.ThreadLocalRandom;
 
-public class SequentialRandomBridgesGenerator implements BridgesGenerator {
+public class BridgesGeneratorBySequentialRandom implements BridgesGenerator {
 
     @Override
     public List<Bridge> generateBridges(Integer numbersOfPeople) {

src/main/java/nextstep/ladder/model/LinesGenerator.java

@@ -6,7 +6,7 @@
 
 public class LinesGenerator {
 
-    private final BridgesGenerator bridgesGenerator = new SequentialRandomBridgesGenerator();
+    private final BridgesGenerator bridgesGenerator = new BridgesGeneratorBySequentialRandom();
 
     public List<Line> generatorLines(Integer numbersOfPeople, Integer height) {
         return IntStream.range(0, height)

src/test/java/nextstep/ladder/model/SequentialRandomBridgesGeneratorTest.java src/test/java/nextstep/ladder/model/BridgesGeneratorBySequentialRandomTest.java

@@ -4,9 +4,9 @@
 
 import org.junit.jupiter.api.Test;
 
-public class SequentialRandomBridgesGeneratorTest {
+public class BridgesGeneratorBySequentialRandomTest {
 
-    private final BridgesGenerator bridgesGenerator = new SequentialRandomBridgesGenerator();
+    private final BridgesGenerator bridgesGenerator = new BridgesGeneratorBySequentialRandom();
 
     @Test
     public void generateBridges_다리_개수_확인() {