Average of Levels in Binary Tree

Author: w2xi

README.md

@@ -72,6 +72,7 @@
 |509|[斐波那契数](https://leetcode.cn/problems/fibonacci-number/)|[JavaScript](./algorithms/fibonacci-number.js)|Easy|
 |543|[二叉树的直径](https://leetcode.cn/problems/diameter-of-binary-tree/)|[JavaScript](./algorithms/diameter-of-binary-tree.js)|Easy|
 |617|[合并二叉树](https://leetcode.cn/problems/merge-two-binary-trees/)|[JavaScript](./algorithms/merge-two-binary-trees.js)|Easy|
+|637|[二叉树的层平均值](https://leetcode.cn/problems/average-of-levels-in-binary-tree/)|[JavaScript](./algorithms/average-of-levels-in-binary-tree.js)|Easy|
 |687|[最长同值路径](https://leetcode.cn/problems/longest-univalue-path/)|[JavaScript](./algorithms/longest-univalue-path.js)|Medium|
 |700|[二叉搜索树中的搜索](https://leetcode.cn/problems/search-in-a-binary-search-tree/)|[JavaScript](./algorithms/search-in-a-binary-search-tree.js)|Easy|
 |704|[二分查找](https://leetcode.cn/problems/binary-search/)|[JavaScript](./algorithms/binary-search.js)|Easy|

algorithms/average-of-levels-in-binary-tree.js

@@ -0,0 +1,59 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * 二叉树的层平均值
+ * @param {TreeNode} root
+ * @return {number[]}
+ */
+var averageOfLevels = function (root) {
+  // 1. DFS
+  let result = [];
+  const dfs = (node, level = 0) => {
+    if (node) {
+      if (!result[level]) result[level] = [];
+      result[level].push(node.val);
+      dfs(node.left, level + 1);
+      dfs(node.right, level + 1);
+    }
+  };
+  dfs(root);
+
+  result = result.map((item) => {
+    const sum = item.reduce((a, b) => a + b);
+    return Number((sum / item.length).toFixed(5));
+  });
+
+  return result;
+
+  // 2. BFS
+  // return bfs(root);
+};
+
+function bfs(root) {
+  const result = [];
+  const queue = [];
+  queue.push(root);
+
+  while (queue.length > 0) {
+    const len = queue.length;
+    let size = len;
+    let sum = 0;
+
+    while (size--) {
+      const node = queue.shift();
+      sum += node.val;
+      node.left && queue.push(node.left);
+      node.right && queue.push(node.right);
+    }
+
+    result.push(Number((sum / len).toFixed(5)));
+  }
+
+  return result;
+}