103 finish

Author: aQua

Algorithms/0103.binary-tree-zigzag-level-order-traversal/README.md

@@ -3,24 +3,24 @@
 ## 题目
 Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between).
 
-
 For example:
 Given binary tree [3,9,20,null,null,15,7],
+```
     3
    / \
   9  20
     /  \
    15   7
-
-
+```
 
 return its zigzag level order traversal as:
+```
 [
   [3],
   [20,9],
   [15,7]
 ]
-
+```
 ## 解题思路
 
 见程序注释

Algorithms/0103.binary-tree-zigzag-level-order-traversal/binary-tree-zigzag-level-order-traversal.go

@@ -8,23 +8,25 @@ type TreeNode = kit.TreeNode
 
 func zigzagLevelOrder(root *TreeNode) [][]int {
 	res := [][]int{}
-	var dfs func(*TreeNode, int)
 
+	var dfs func(*TreeNode, int)
 	dfs = func(root *TreeNode, level int) {
 		if root == nil {
 			return
 		}
-
 		// 出现了新的 level
 		if level >= len(res) {
 			res = append(res, []int{})
 		}
+		// 与 102 题相比，level 的奇偶不同，append 会不同。
 		if level%2 == 0 {
 			res[level] = append(res[level], root.Val)
 		} else {
-			res[level] = append([]int{root.Val}, res[level]...)
+			temp := make([]int ,  len(res[level])+1)
+			temp[0] = root.Val
+			copy(temp[1:], res[level])
+			res[level] = temp
 		}
-
 		dfs(root.Left, level+1)
 		dfs(root.Right, level+1)
 	}