规范格式

leetcode/0105.Construct-Binary-Tree-from-Preorder-and-Inorder-Traversal/105. Construct Binary Tree from Preorder and Inorder Traversal.go

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+package leetcode
+
+import (
+	"github.com/halfrost/LeetCode-Go/structures"
+)
+
+// TreeNode define
+type TreeNode = structures.TreeNode
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+
+func buildTree(preorder []int, inorder []int) *TreeNode {
+	inPos := make(map[int]int)
+	for i := 0; i < len(inorder); i++ {
+		inPos[inorder[i]] = i
+	}
+	return buildPreIn2TreeDFS(preorder, 0, len(preorder)-1, 0, inPos)
+}
+
+func buildPreIn2TreeDFS(pre []int, preStart int, preEnd int, inStart int, inPos map[int]int) *TreeNode {
+	if preStart > preEnd {
+		return nil
+	}
+	root := &TreeNode{Val: pre[preStart]}
+	rootIdx := inPos[pre[preStart]]
+	leftLen := rootIdx - inStart
+	root.Left = buildPreIn2TreeDFS(pre, preStart+1, preStart+leftLen, inStart, inPos)
+	root.Right = buildPreIn2TreeDFS(pre, preStart+leftLen+1, preEnd, rootIdx+1, inPos)
+	return root
+}

leetcode/0105.Construct-Binary-Tree-from-Preorder-and-Inorder-Traversal/105. Construct Binary Tree from Preorder and Inorder Traversal_test.go

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+package leetcode
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/halfrost/LeetCode-Go/structures"
+)
+
+type question105 struct {
+	para105
+	ans105
+}
+
+// para 是参数
+// one 代表第一个参数
+type para105 struct {
+	preorder []int
+	inorder  []int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans105 struct {
+	one []int
+}
+
+func Test_Problem105(t *testing.T) {
+
+	qs := []question105{
+
+		question105{
+			para105{[]int{3, 9, 20, 15, 7}, []int{9, 3, 15, 20, 7}},
+			ans105{[]int{3, 9, 20, structures.NULL, structures.NULL, 15, 7}},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 105------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans105, q.para105
+		fmt.Printf("【input】:%v      ", p)
+		fmt.Printf("【output】:%v      \n", structures.Tree2ints(buildTree(p.preorder, p.inorder)))
+	}
+	fmt.Printf("\n\n\n")
+}

leetcode/0105.Construct-Binary-Tree-from-Preorder-and-Inorder-Traversal/README.md

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+# [105. Construct Binary Tree from Preorder and Inorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/)
+
+
+## 题目:
+
+Given preorder and inorder traversal of a tree, construct the binary tree.
+
+**Note:**You may assume that duplicates do not exist in the tree.
+
+For example, given
+
+    preorder = [3,9,20,15,7]
+    inorder = [9,3,15,20,7]
+
+Return the following binary tree:
+
+    		3
+       / \
+      9  20
+        /  \
+       15   7
+
+
+
+## 题目大意
+
+根据一棵树的前序遍历与中序遍历构造二叉树。
+
+注意:
+你可以假设树中没有重复的元素。
+
+
+## 解题思路
+
+- 给出 2 个数组，根据 preorder 和 inorder 数组构造一颗树。
+- 利用递归思想，从 preorder 可以得到根节点，从 inorder 中得到左子树和右子树。只剩一个节点的时候即为根节点。不断的递归直到所有的树都生成完成。