leetcode week2-4

Author: bus710

construct-binary-tree-from-preorder-and-inorder-traversal/bus710.go

@@ -0,0 +1,105 @@
+package hello
+
+import (
+	"errors"
+	"log"
+)
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func buildTree(preorder []int, inorder []int) *TreeNode {
+	if len(preorder) == 1 {
+		return &TreeNode{
+			Val: preorder[0],
+		}
+	}
+
+	center, _ := findCenterWithValue(preorder[0], inorder)
+
+	head := TreeNode{
+		Val: inorder[center],
+	}
+
+	execute(&head, center, inorder)
+
+	return &head
+}
+
+func findCenterWithValue(key int, inorder []int) (int, error) {
+	for i, n := range inorder {
+		if n == key {
+			return i, nil
+		}
+	}
+	return 0, errors.New("not found")
+}
+
+func findCenter(slice []int) int {
+	c := len(slice) / 2
+	return c
+}
+
+func getSplit(center int, inorder []int, currentVal int) ([]int, []int) {
+	if len(inorder) == 1 {
+		if inorder[0] == currentVal {
+			return nil, nil
+		}
+		return []int{inorder[0]}, nil
+	}
+	if len(inorder) == 2 {
+		if inorder[0] == currentVal {
+			return nil, []int{inorder[1]}
+		}
+		if inorder[1] == currentVal {
+			return []int{inorder[0]}, nil
+		}
+		return []int{inorder[0]}, []int{inorder[1]}
+	}
+	return inorder[:center], inorder[center+1:]
+}
+
+func execute(currentNode *TreeNode, center int, slice []int) {
+	left, right := getSplit(center, slice, currentNode.Val)
+
+	if len(left) == 1 {
+		currentNode.Left = &TreeNode{Val: left[0]}
+	} else if len(left) == 2 {
+		currentNode.Left = &TreeNode{Val: left[0]}
+		currentNode.Left.Right = &TreeNode{Val: left[1]}
+	} else if len(left) > 2 {
+		lc := findCenter(left)
+		currentNode.Left = &TreeNode{Val: left[lc]}
+
+		if len(left) > 2 {
+			execute(currentNode.Left, lc, left)
+		}
+	}
+
+	if len(right) == 1 {
+		currentNode.Right = &TreeNode{Val: right[0]}
+	} else if len(right) == 2 {
+		currentNode.Right = &TreeNode{Val: right[0]}
+		currentNode.Right.Left = &TreeNode{Val: right[1]}
+	} else if len(right) > 2 {
+		rc := findCenter(right)
+		currentNode.Right = &TreeNode{Val: right[rc]}
+
+		if len(right) > 2 {
+			execute(currentNode.Right, rc, right)
+		}
+	}
+}
+
+func print(currentNode *TreeNode) {
+	log.Println(currentNode.Val)
+	if currentNode.Left != nil {
+		print(currentNode.Left)
+	}
+	if currentNode.Right != nil {
+		print(currentNode.Right)
+	}
+}