Create 341. Flatten Nested List Iterator

Author: rajatag03

341. Flatten Nested List Iterator

@@ -0,0 +1,55 @@
+/**
+ * // 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 empty list if this NestedInteger holds a single integer
+ *     public List<NestedInteger> getList();
+ * }
+ */
+public class NestedIterator implements Iterator<Integer> {
+
+    List<Integer> flattenList = null;
+    int current=0;
+    public NestedIterator(List<NestedInteger> nestedList) {
+        flattenList= new ArrayList<>();
+        for(NestedInteger integer:nestedList){
+            helper(integer);
+        }
+    }
+
+    @Override
+    public Integer next() {
+        return flattenList.get(current++);
+    }
+
+    @Override
+    public boolean hasNext() {
+        return current<flattenList.size();
+    }
+    
+    private void helper(NestedInteger value){
+        if(value.isInteger()){
+            flattenList.add(value.getInteger());
+        }
+        else{
+            for(NestedInteger integer:value.getList()){
+                helper(integer);
+            }
+        }
+    }
+}
+
+/**
+ * Your NestedIterator object will be instantiated and called as such:
+ * NestedIterator i = new NestedIterator(nestedList);
+ * while (i.hasNext()) v[f()] = i.next();
+ */