107 accepted. 6ms.

Author: aQua

Algorithms/0107.binary-tree-level-order-traversal-ii/README.md

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+# [107. Binary Tree Level Order Traversal II](https://leetcode.com/problems/binary-tree-level-order-traversal-ii/)
+
+## 题目
+Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).
+
+
+For example:
+Given binary tree [3,9,20,null,null,15,7],
+```
+    3
+   / \
+  9  20
+    /  \
+   15   7
+```
+
+return its bottom-up level order traversal as:
+```
+[
+  [15,7],
+  [9,20],
+  [3]
+]
+```
+
+## 解题思路
+
+见程序注释

Algorithms/0107.binary-tree-level-order-traversal-ii/binary-tree-level-order-traversal-ii.go

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+package Problem0107
+
+import (
+	"github.com/aQuaYi/LeetCode-in-Golang/kit"
+)
+
+type TreeNode =  kit.TreeNode
+
+func levelOrderBottom(root *TreeNode) [][]int {
+	temp := [][]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(temp)   {
+			temp = append(temp, []int{})
+		}
+		temp[level] = append(temp[level], root.Val)
+
+		dfs(root.Left, level+1)
+		dfs(root.Right, level+1)
+	}
+
+	dfs(root, 0)
+
+	n  := len(temp )
+	res := make([][]int , n )
+	for i:=0; i<n ; i++{
+		res[i] = temp[n-i-1]
+	}
+
+	return res 
+}

Algorithms/0107.binary-tree-level-order-traversal-ii/binary-tree-level-order-traversal-ii_test.go

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+package Problem0107
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/aQuaYi/LeetCode-in-Golang/kit"
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_Problem0107(t *testing.T) {
+	ast := assert.New(t)
+
+	// tcs is testcase slice
+	tcs := []struct {
+		pre, in []int
+		ans     [][]int
+	}{
+
+		{
+			[]int{3, 9, 20, 15, 7},
+			[]int{9, 3, 15, 20, 7},
+			[][]int{
+				[]int{15, 7},
+				[]int{9, 20},
+				[]int{3},
+			},
+		},
+
+		// 可以多个 testcase
+	}
+
+	for _, tc := range tcs {
+		fmt.Printf("~~%v~~\n", tc)
+
+		ast.Equal(tc.ans, levelOrderBottom(kit.PreIn2Tree(tc.pre, tc.in)), "输入:%v", tc)
+	}
+}