flatten nestlist + minor refactorings: done

Author: rampatra

src/main/java/com/leetcode/recursion/FlattenNestListIterator.java

@@ -0,0 +1,69 @@
+package com.leetcode.recursion;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+/**
+ * Level: Medium
+ * Link: https://leetcode.com/problems/flatten-nested-list-iterator/
+ * Description:
+ * Given a nested list of integers, implement an iterator to flatten it.
+ *
+ * Each element is either an integer, or a list -- whose elements may also be integers or other lists.
+ *
+ * Example 1:
+ * Input: [[1,1],2,[1,1]]
+ * Output: [1,1,2,1,1]
+ * Explanation: By calling next repeatedly until hasNext returns false,
+ *              the order of elements returned by next should be: [1,1,2,1,1].
+ *
+ * Example 2:
+ * Input: [1,[4,[6]]]
+ * Output: [1,4,6]
+ * Explanation: By calling next repeatedly until hasNext returns false,
+ *              the order of elements returned by next should be: [1,4,6].
+ *
+ * Runtime: <a href="https://leetcode.com/submissions/detail/250996020/">2 ms</a>.
+ *
+ * @author rampatra
+ * @since 2019-08-12
+ */
+public class FlattenNestListIterator implements Iterator<Integer> {
+
+    private int index;
+    private List<Integer> flattenedList;
+
+    public FlattenNestListIterator(List<NestedInteger> nestedList) {
+        index = 0;
+        flattenedList = getFlattenedList(nestedList);
+    }
+
+    private List<Integer> getFlattenedList(List<NestedInteger> nestedList) {
+        List<Integer> flattenedList = new ArrayList<>();
+
+        for (NestedInteger nestedInteger : nestedList) {
+            if (nestedInteger.isInteger()) {
+                flattenedList.add(nestedInteger.getInteger());
+            } else {
+                flattenedList.addAll(getFlattenedList(nestedInteger.getList()));
+            }
+        }
+
+        return flattenedList;
+    }
+
+    @Override
+    public Integer next() {
+        return flattenedList.get(index++);
+    }
+
+    @Override
+    public boolean hasNext() {
+        return index < flattenedList.size();
+    }
+
+    public static void main(String[] args) {
+        // TODO add some test cases
+    }
+}

src/main/java/com/leetcode/recursion/NestedInteger.java

@@ -0,0 +1,46 @@
+package com.leetcode.recursion;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Class needed for various problems like {@link NestedListWeightSumII}, {@link FlattenNestListIterator}, etc.
+ *
+ * @author rampatra
+ * @since 2019-08-12
+ */
+public class NestedInteger {
+
+    private Integer integer;
+    private List<NestedInteger> list;
+
+    public NestedInteger() {
+        this.list = new ArrayList<>();
+    }
+
+    public NestedInteger(int integer) {
+        this.integer = integer;
+        this.list = new ArrayList<>();
+    }
+
+    public boolean isInteger() {
+        return this.integer != null;
+    }
+
+    public Integer getInteger() {
+        return integer;
+    }
+
+    public void setInteger(Integer integer) {
+        this.integer = integer;
+    }
+
+    public List<NestedInteger> getList() {
+        return list;
+    }
+
+    public NestedInteger add(NestedInteger nestedInteger) {
+        this.list.add(nestedInteger);
+        return this;
+    }
+}

src/main/java/com/leetcode/arrays/NestedListWeightSum.java renamed to src/main/java/com/leetcode/recursion/NestedListWeightSum.java

@@ -1,4 +1,4 @@
-package com.leetcode.arrays;
+package com.leetcode.recursion;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 

src/main/java/com/leetcode/arrays/NestedListWeightSumII.java renamed to src/main/java/com/leetcode/recursion/NestedListWeightSumII.java

@@ -1,4 +1,4 @@
-package com.leetcode.arrays;
+package com.leetcode.recursion;
 
 import java.util.*;
 
@@ -77,40 +77,4 @@ public static void main(String[] args) {
 
         assertEquals(17, nestedSum(Collections.singletonList(ni)));
     }
-}
-
-class NestedInteger {
-
-    private Integer integer;
-    private List<NestedInteger> list;
-
-    public NestedInteger() {
-        this.list = new ArrayList<>();
-    }
-
-    public NestedInteger(int integer) {
-        this.integer = integer;
-        this.list = new ArrayList<>();
-    }
-
-    public boolean isInteger() {
-        return this.integer != null;
-    }
-
-    public Integer getInteger() {
-        return integer;
-    }
-
-    public void setInteger(Integer integer) {
-        this.integer = integer;
-    }
-
-    public List<NestedInteger> getList() {
-        return list;
-    }
-
-    public NestedInteger add(NestedInteger nestedInteger) {
-        this.list.add(nestedInteger);
-        return this;
-    }
 }