102. 二叉树的层次遍历打卡

V1ncentzzZ · web-flow · commit 35018d740f94 · 2018-12-06T17:57:46.000+08:00
diff --git a/2018.12.05-leetcode102/。V1ncentzzZ.md b/2018.12.05-leetcode102/。V1ncentzzZ.md
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+[102. 二叉树的层次遍历] (https://leetcode-cn.com/problems/binary-tree-level-order-traversal/)
+
+给定一个二叉树，返回其按层次遍历的节点值。 （即逐层地，从左到右访问所有节点）。
+
+例如:
+给定二叉树: [3,9,20,null,null,15,7],
+
+    3
+   / \
+  9  20
+    /  \
+   15   7
+返回其层次遍历结果：
+
+[
+  [3],
+  [9,20],
+  [15,7]
+]
+
+
+```
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+ // TODO 解题关键：传递树高度
+class Solution {
+    public List<List<Integer>> levelOrder(TreeNode root) {
+        List<List<Integer>> result = new ArrayList<>();
+        if(root == null) return result;
+        executor(root,result,0);
+        return result;    
+    }
+    
+    public void executor(TreeNode node,List<List<Integer>> result,int high){
+        if(node == null) return;
+        if(result.size() < high+1) result.add(new ArrayList<>());
+        result.get(high).add(node.val);
+        high++;
+        executor(node.left,result,high);
+        executor(node.right,result,high);
+    }
+}
+```
