feat: 二叉树层次遍历

Author: sl1673495

二叉树/107. 二叉树的层次遍历 II.js

@@ -0,0 +1,40 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+
+let TreeNode = require('../工具/二叉树.js')
+
+/**
+ * @param {TreeNode} root
+ * @return {number[][]}
+ */
+var levelOrderBottom = function (root) {
+  let res = []
+  let dfs = (node, level = 0) => {
+      if (!node) return
+
+      if (!res[level]) {
+          res[level] = []
+      }
+
+      dfs(node.left, level + 1)
+      dfs(node.right, level + 1)
+
+      res[level].push(node.val)
+  }
+
+  dfs(root)
+  return res.reverse()
+};
+
+var t = new TreeNode(3)
+t.left = new TreeNode(9)
+t.right = new TreeNode(20)
+t.right.left = new TreeNode(15)
+t.right.right = new TreeNode(7)
+
+console.log(levelOrderBottom(t))