添加 problem 144

Algorithms/144. Binary Tree Preorder Traversal/144. Binary Tree Preorder Traversal.go

@@ -0,0 +1,39 @@
+package leetcode
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func preorderTraversal(root *TreeNode) []int {
+	res := []int{}
+	if root != nil {
+		res = append(res, root.Val)
+		tmp := preorderTraversal(root.Left)
+		for _, t := range tmp {
+			res = append(res, t)
+		}
+		tmp = preorderTraversal(root.Right)
+		for _, t := range tmp {
+			res = append(res, t)
+		}
+	}
+	return res
+}
+
+func preorderTraversal_(root *TreeNode) []int {
+	var result []int
+	preorder(root, &result)
+	return result
+}
+
+func preorder(root *TreeNode, output *[]int) {
+	if root != nil {
+		*output = append(*output, root.Val)
+		preorder(root.Left, output)
+		preorder(root.Right, output)
+	}
+}

Algorithms/144. Binary Tree Preorder Traversal/144. Binary Tree Preorder Traversal_test.go

@@ -0,0 +1,213 @@
+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question144 struct {
+	para144
+	ans144
+}
+
+// para 是参数
+// one 代表第一个参数
+type para144 struct {
+	one []int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans144 struct {
+	one []int
+}
+
+func Test_Problem144(t *testing.T) {
+
+	qs := []question144{
+
+		question144{
+			para144{[]int{}},
+			ans144{[]int{}},
+		},
+
+		question144{
+			para144{[]int{1}},
+			ans144{[]int{1}},
+		},
+
+		question144{
+			para144{[]int{1, NULL, 2, 3}},
+			ans144{[]int{1, 2, 3}},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 144------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans144, q.para144
+		fmt.Printf("【input】:%v      ", p)
+		root := Ints2TreeNode(p.one)
+		fmt.Printf("【output】:%v      \n", preorderTraversal(root))
+	}
+	fmt.Printf("\n\n\n")
+}
+
+var NULL = -1 << 63
+
+// Ints2TreeNode 利用 []int 生成 *TreeNode
+func Ints2TreeNode(ints []int) *TreeNode {
+	n := len(ints)
+	if n == 0 {
+		return nil
+	}
+	root := &TreeNode{
+		Val: ints[0],
+	}
+	queue := make([]*TreeNode, 1, n*2)
+	queue[0] = root
+	i := 1
+	for i < n {
+		node := queue[0]
+		queue = queue[1:]
+		if i < n && ints[i] != NULL {
+			node.Left = &TreeNode{Val: ints[i]}
+			queue = append(queue, node.Left)
+		}
+		i++
+		if i < n && ints[i] != NULL {
+			node.Right = &TreeNode{Val: ints[i]}
+			queue = append(queue, node.Right)
+		}
+		i++
+	}
+	return root
+}
+
+func indexOf(val int, nums []int) int {
+	for i, v := range nums {
+		if v == val {
+			return i
+		}
+	}
+
+	msg := fmt.Sprintf("%d 不存在于 %v 中", val, nums)
+	panic(msg)
+}
+
+// PreIn2Tree 把 preorder 和 inorder 切片转换成 二叉树
+func PreIn2Tree(pre, in []int) *TreeNode {
+	if len(pre) != len(in) {
+		panic("preIn2Tree 中两个切片的长度不相等")
+	}
+	if len(in) == 0 {
+		return nil
+	}
+	res := &TreeNode{
+		Val: pre[0],
+	}
+	if len(in) == 1 {
+		return res
+	}
+	idx := indexOf(res.Val, in)
+	res.Left = PreIn2Tree(pre[1:idx+1], in[:idx])
+	res.Right = PreIn2Tree(pre[idx+1:], in[idx+1:])
+	return res
+}
+
+// InPost2Tree 把 inorder 和 postorder 切片转换成 二叉树
+func InPost2Tree(in, post []int) *TreeNode {
+	if len(post) != len(in) {
+		panic("inPost2Tree 中两个切片的长度不相等")
+	}
+	if len(in) == 0 {
+		return nil
+	}
+	res := &TreeNode{
+		Val: post[len(post)-1],
+	}
+	if len(in) == 1 {
+		return res
+	}
+	idx := indexOf(res.Val, in)
+	res.Left = InPost2Tree(in[:idx], post[:idx])
+	res.Right = InPost2Tree(in[idx+1:], post[idx:len(post)-1])
+	return res
+}
+
+// Tree2Preorder 把 二叉树 转换成 preorder 的切片
+func Tree2Preorder(root *TreeNode) []int {
+	if root == nil {
+		return nil
+	}
+	if root.Left == nil && root.Right == nil {
+		return []int{root.Val}
+	}
+	res := []int{root.Val}
+	res = append(res, Tree2Preorder(root.Left)...)
+	res = append(res, Tree2Preorder(root.Right)...)
+	return res
+}
+
+// Tree2Inorder 把 二叉树转换成 inorder 的切片
+func Tree2Inorder(root *TreeNode) []int {
+	if root == nil {
+		return nil
+	}
+	if root.Left == nil && root.Right == nil {
+		return []int{root.Val}
+	}
+	res := Tree2Inorder(root.Left)
+	res = append(res, root.Val)
+	res = append(res, Tree2Inorder(root.Right)...)
+	return res
+}
+
+// Tree2Postorder 把 二叉树 转换成 postorder 的切片
+func Tree2Postorder(root *TreeNode) []int {
+	if root == nil {
+		return nil
+	}
+	if root.Left == nil && root.Right == nil {
+		return []int{root.Val}
+	}
+	res := Tree2Postorder(root.Left)
+	res = append(res, Tree2Postorder(root.Right)...)
+	res = append(res, root.Val)
+	return res
+}
+
+// Equal return ture if tn == a
+func (tn *TreeNode) Equal(a *TreeNode) bool {
+	if tn == nil && a == nil {
+		return true
+	}
+	if tn == nil || a == nil || tn.Val != a.Val {
+		return false
+	}
+	return tn.Left.Equal(a.Left) && tn.Right.Equal(a.Right)
+}
+
+// Tree2ints 把 *TreeNode 按照行还原成 []int
+func Tree2ints(tn *TreeNode) []int {
+	res := make([]int, 0, 1024)
+	queue := []*TreeNode{tn}
+	for len(queue) > 0 {
+		size := len(queue)
+		for i := 0; i < size; i++ {
+			nd := queue[i]
+			if nd == nil {
+				res = append(res, NULL)
+			} else {
+				res = append(res, nd.Val)
+				queue = append(queue, nd.Left, nd.Right)
+			}
+		}
+		queue = queue[size:]
+	}
+	i := len(res)
+	for i > 0 && res[i-1] == NULL {
+		i--
+	}
+	return res[:i]
+}

Algorithms/144. Binary Tree Preorder Traversal/README.md

@@ -0,0 +1,33 @@
+# [144. Binary Tree Preorder Traversal](https://leetcode.com/problems/binary-tree-preorder-traversal/)
+
+## 题目
+
+Given a binary tree, return the preorder traversal of its nodes' values.
+
+
+
+Example :
+
+```c
+Input: [1,null,2,3]
+   1
+    \
+     2
+    /
+   3
+
+Output: [1,2,3]
+```
+
+
+Follow up: Recursive solution is trivial, could you do it iteratively?
+
+
+ 
+
+## 题目大意
+
+先根遍历一颗树。两种递归的实现方法，见代码。
+
+
+