flattening using recursion

Author: Arjiit

nestedIterator.java

@@ -0,0 +1,53 @@
+/**
+ * // This is the interface that allows for creating nested lists.
+ * // You should not implement it, or speculate about its implementation
+ * public interface NestedInteger {
+ *
+ *     // @return true if this NestedInteger holds a single integer, rather than a nested list.
+ *     public boolean isInteger();
+ *
+ *     // @return the single integer that this NestedInteger holds, if it holds a single integer
+ *     // Return null if this NestedInteger holds a nested list
+ *     public Integer getInteger();
+ *
+ *     // @return the nested list that this NestedInteger holds, if it holds a nested list
+ *     // Return null if this NestedInteger holds a single integer
+ *     public List<NestedInteger> getList();
+ * }
+ */
+public class NestedIterator implements Iterator<Integer> {
+    List<Integer> list;
+    int i=0;
+    public NestedIterator(List<NestedInteger> nestedList) {
+        list = getList(nestedList, new ArrayList<>());
+    }
+    
+    public List<Integer> getList(List<NestedInteger> list, List<Integer> output) {
+        for(NestedInteger n: list) {
+            if (n.isInteger()) {
+                output.add(n.getInteger());
+            } else {
+                getList(n.getList(), output);
+            }
+        }
+        return output;
+    }
+
+    @Override
+    public Integer next() {
+        return list.get(i++);
+    }
+
+    @Override
+    public boolean hasNext() {
+        if (i == list.size())
+            return false;
+        return true;
+    }
+}
+
+/**
+ * Your NestedIterator object will be instantiated and called as such:
+ * NestedIterator i = new NestedIterator(nestedList);
+ * while (i.hasNext()) v[f()] = i.next();
+ */