Create 339. Nested List Weight Sum.java

Author: futurus

339. Nested List Weight Sum.java

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+/**
+ * // 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 Solution {
+    public int helper(List<NestedInteger> nl, int depth) {
+        int sum = 0;
+        for (int i = 0; i < nl.size(); i++) {
+            if (nl.get(i).isInteger()) {
+                sum += nl.get(i).getInteger() * depth;
+            } else {
+                sum += helper(nl.get(i).getList(), depth+1);
+            }
+        }
+        return sum;
+    }
+    
+    public int depthSum(List<NestedInteger> nestedList) {
+        return helper(nestedList, 1);
+    }
+}