590. N 叉树的后序遍历

Author: w2xi

README.md

@@ -127,6 +127,7 @@
 |557|[反转字符串中的单词 III](https://leetcode.cn/problems/reverse-words-in-a-string-iii/)|[JavaScript](./algorithms/reverse-words-in-a-string-iii.js)|Easy|
 |566|[重塑矩阵](https://leetcode.cn/problems/reshape-the-matrix/)|[JavaScript](./algorithms/reshape-the-matrix.js)|Easy|
 |589|[N 叉树的前序遍历](https://leetcode.cn/problems/n-ary-tree-preorder-traversal/)|[JavaScript](./algorithms/n-ary-tree-preorder-traversal.js)|Easy|
+|590|[N 叉树的后序遍历](https://leetcode.cn/problems/n-ary-tree-postorder-traversal/)|[JavaScript](./algorithms/n-ary-tree-postorder-traversal.js)|Easy|
 |598|[范围求和 II](https://leetcode.cn/problems/range-addition-ii/)|[JavaScript](./algorithms/range-addition-ii.js)|Easy|
 |617|[合并二叉树](https://leetcode.cn/problems/merge-two-binary-trees/)|[JavaScript](./algorithms/merge-two-binary-trees.js)|Easy|
 |628|[三个数的最大乘积](https://leetcode.cn/problems/maximum-product-of-three-numbers/)|[JavaScript](./algorithms/maximum-product-of-three-numbers.js)|Easy|

algorithms/n-ary-tree-postorder-traversal.js

@@ -0,0 +1,53 @@
+/**
+ * // Definition for a Node.
+ * function Node(val,children) {
+ *    this.val = val;
+ *    this.children = children;
+ * };
+ */
+
+/**
+ * @param {Node|null} root
+ * @return {number[]}
+ */
+var postorder = function (root) {
+  // DFS
+  const result = [];
+  const dfs = (node) => {
+    if (node) {
+      const children = node.children;
+      children.forEach((child) => {
+        dfs(child);
+      });
+      result.push(node.val);
+    }
+  };
+
+  dfs(root);
+
+  return result;
+
+  // BFS
+  // return bfs(root);
+};
+
+// 后序遍历 左右中
+// 先序遍历(中左右) -> 中右左(调整代码顺序) -> 左右中(反转结果)
+
+function bfs(root) {
+  if (!root) return [];
+  const result = [];
+  const stack = [];
+  stack.push(root);
+
+  while (stack.length) {
+    const node = stack.pop();
+    result.push(node.val);
+    const children = node.children;
+    children.forEach((child) => {
+      stack.push(child);
+    });
+  }
+
+  return result.reverse();
+}