add 590

fishercoder1534 · fishercoder1534 · commit 153ebaec32e6 · 2018-12-21T09:39:53.000-08:00
diff --git a/README.md b/README.md
@@ -191,6 +191,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |593|[Valid Square](https://leetcode.com/problems/valid-square/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_593.java) | O(1) |O(1) | |Medium | Math
 |592|[Fraction Addition and Subtraction](https://leetcode.com/problems/fraction-addition-and-subtraction/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_592.java) | O(nlogx) |O(n) | |Medium | Math
 |591|[Tag Validator](https://leetcode.com/problems/tag-validator/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_591.java) | O(n) |O(n) | |Hard | Stack, String
+|590|[N-ary Tree Postorder Traversal](https://leetcode.com/problems/n-ary-tree-postorder-traversal/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_590.java) | O(n) |O(n) | |Easy| DFS, recursion
 |589|[N-ary Tree Preorder Traversal](https://leetcode.com/problems/n-ary-tree-preorder-traversal/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_589.java) | O(n) |O(n) | |Easy | DFS, recursion
 |588|[Design In-Memory File System](https://leetcode.com/problems/design-in-memory-file-system/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_588.java) | O(n) |O(h) | |Hard | Trie, Design
 |587|[Erect the Fence](https://leetcode.com/problems/erect-the-fence/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_587.java) | O(?) |O(?) | |Hard | Geometry
diff --git a/src/main/java/com/fishercoder/solutions/_590.java b/src/main/java/com/fishercoder/solutions/_590.java
@@ -0,0 +1,50 @@
+package com.fishercoder.solutions;
+
+import com.fishercoder.common.classes.Node;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 590. N-ary Tree Postorder Traversal
+ *
+ * Given an n-ary tree, return the postorder traversal of its nodes' values.
+ *
+ * For example, given a 3-ary tree:
+ *
+ *              1
+ *            / | \
+ *           3  2  4
+ *          / \
+ *         5   6
+ *
+ * Return its postorder traversal as: [5,6,3,2,4,1].
+ *
+ * Note:
+ *
+ * Recursive solution is trivial, could you do it iteratively?
+ */
+public class _590 {
+  public static class Solution1 {
+    public List<Integer> postorder(Node root) {
+      List<Integer> result = new ArrayList<>();
+      if (root == null) {
+        return result;
+      }
+      dfs(root, result);
+      result.add(root.val);
+      return result;
+    }
+
+    private void dfs(Node root, List<Integer> result) {
+      if (root == null) {
+        return;
+      }
+      if (root.children.size() > 0) {
+        for (Node child : root.children) {
+          dfs(child, result);
+          result.add(child.val);
+        }
+      }
+    }
+  }
+}
