Solved the issue #253

leetcode/0114.Flatten-Binary-Tree-to-Linked-List/114. Flatten Binary Tree to Linked List.go

@@ -18,23 +18,21 @@ type TreeNode = structures.TreeNode
 
 // 解法一 非递归
 func flatten(root *TreeNode) {
-	list, cur := []int{}, &TreeNode{}
-	preorder(root, &list)
-	cur = root
+	list := preorder(root)
 	for i := 1; i < len(list); i++ {
-		cur.Left = nil
-		cur.Right = &TreeNode{Val: list[i], Left: nil, Right: nil}
-		cur = cur.Right
+		prev, cur := list[i-1], list[i]
+		prev.Left, prev.Right = nil, cur
 	}
 	return
 }
 
-func preorder(root *TreeNode, output *[]int) {
+func preorder(root *TreeNode) (ans []*TreeNode) {
 	if root != nil {
-		*output = append(*output, root.Val)
-		preorder(root.Left, output)
-		preorder(root.Right, output)
+		ans = append(ans, root)
+		ans = append(ans, preorder(root.Left)...)
+		ans = append(ans, preorder(root.Right)...)
 	}
+	return
 }
 
 // 解法二 递归

leetcode/0114.Flatten-Binary-Tree-to-Linked-List/114. Flatten Binary Tree to Linked List_test.go

@@ -15,13 +15,13 @@ type question114 struct {
 // para 是参数
 // one 代表第一个参数
 type para114 struct {
-	one []int
+	one []string
 }
 
 // ans 是答案
 // one 代表第一个答案
 type ans114 struct {
-	one []int
+	one []string
 }
 
 func Test_Problem114(t *testing.T) {
@@ -29,8 +29,18 @@ func Test_Problem114(t *testing.T) {
 	qs := []question114{
 
 		{
-			para114{[]int{1, 2, 3, 4, 5, 6}},
-			ans114{[]int{1, 2, 3, 4, 5, 6}},
+			para114{[]string{"1", "2", "5", "3", "4", "null", "6"}},
+			ans114{[]string{"1", "null", "2", "null", "3", "null", "4", "null", "5", "null", "6"}},
+		},
+
+		{
+			para114{[]string{"0"}},
+			ans114{[]string{"0"}},
+		},
+
+		{
+			para114{[]string{"1", "2", "3", "4", "5", "6"}},
+			ans114{[]string{"1", "2", "4", "5", "3", "6", "null"}},
 		},
 	}
 
@@ -39,9 +49,10 @@ func Test_Problem114(t *testing.T) {
 	for _, q := range qs {
 		_, p := q.ans114, q.para114
 		fmt.Printf("【input】:%v       \n", p)
-		rootOne := structures.Ints2TreeNode(p.one)
+		rootOne := structures.Strings2TreeNode(p.one)
 		flatten(rootOne)
-		fmt.Printf("【output】:%v      \n", structures.Tree2Preorder(rootOne))
+		fmt.Printf("【levelorder output】:%v       \n", structures.Tree2LevelOrderStrings(rootOne))
+		fmt.Printf("【preorder output】:%v      \n", structures.Tree2PreOrderStrings(rootOne))
 	}
 	fmt.Printf("\n\n\n")
 }

structures/TreeNode.go

@@ -2,6 +2,7 @@ package structures
 
 import (
 	"fmt"
+	"strconv"
 )
 
 // TreeNode is tree's node
@@ -218,7 +219,7 @@ func Tree2ints(tn *TreeNode) []int {
 	return res[:i]
 }
 
-// T2s convert *TreeNode to []int
+// T2s converts *TreeNode to []int
 func T2s(head *TreeNode, array *[]int) {
 	fmt.Printf("运行到这里了 head = %v array = %v\n", head, array)
 	// fmt.Printf("****array = %v\n", array)
@@ -231,3 +232,83 @@ func T2s(head *TreeNode, array *[]int) {
 		T2s(head.Right, array)
 	}
 }
+
+// Strings2TreeNode converts []string to *TreeNode
+func Strings2TreeNode(strs []string) *TreeNode {
+	n := len(strs)
+	if n == 0 {
+		return nil
+	}
+	x, _ := strconv.Atoi(strs[0])
+	root := &TreeNode{Val: x}
+	queue := make([]*TreeNode, 1, n<<1)
+	queue[0] = root
+	i := 1
+	for i < n {
+		node := queue[0]
+		queue = queue[1:]
+		if i < n && strs[i] != "null" {
+			x, _ = strconv.Atoi(strs[i])
+			node.Left = &TreeNode{Val: x}
+			queue = append(queue, node.Left)
+		}
+		i++
+		if i < n && strs[i] != "null" {
+			x, _ = strconv.Atoi(strs[i])
+			node.Right = &TreeNode{Val: x}
+			queue = append(queue, node.Right)
+		}
+		i++
+	}
+	return root
+}
+
+// Tree2LevelOrderStrings converts *TreeNode into []string by level order traversal.
+func Tree2LevelOrderStrings(root *TreeNode) []string {
+	var ans []string
+	if root == nil {
+		return ans
+	}
+	queue := []*TreeNode{root}
+	var level int
+	for level = 0; len(queue) > 0; level++ {
+		size := len(queue)
+		for i := 0; i < size; i++ {
+			node := queue[i]
+			if node == nil {
+				ans = append(ans, "null")
+			} else {
+				ans = append(ans, strconv.Itoa(node.Val))
+				if node.Left != nil || node.Right != nil {
+					queue = append(queue, node.Left, node.Right)
+				}
+			}
+		}
+		queue = queue[size:]
+	}
+	level--
+	return ans
+}
+
+// Tree2PreOrderStrings converts *TreeNode into []string by preorder traversal.
+func Tree2PreOrderStrings(root *TreeNode) []string {
+	var ans []string
+	if root == nil {
+		return ans
+	}
+	stack := []*TreeNode{root}
+	node := root
+	for len(stack) > 0 {
+		if node == nil {
+			ans = append(ans, "null")
+		}
+		for node != nil {
+			ans = append(ans, strconv.Itoa(node.Val))
+			stack = append(stack, node)
+			node = node.Left
+		}
+		node = stack[len(stack)-1].Right
+		stack = stack[:len(stack)-1]
+	}
+	return ans
+}