add new solutions

solutions/1/q105/solution.go

@@ -0,0 +1,35 @@
+package q105
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func bld(preorder []int, inorder map[int]int, pL, pR, iL, iR int) *TreeNode {
+	if pL == pR {
+		return nil
+	}
+
+	val := preorder[pL]
+	p := inorder[val] // position of val in "inorder"
+
+	left := bld(preorder, inorder, pL+1, pL+1+p-iL, iL, p)
+	right := bld(preorder, inorder, pL+1+p-iL, pR, p+1, iR)
+
+	return &TreeNode{
+		Val:   val,
+		Left:  left,
+		Right: right,
+	}
+}
+
+func buildTree(preorder []int, inorder []int) *TreeNode {
+	iIdx := make(map[int]int, len(inorder))
+	for i := range inorder {
+		iIdx[inorder[i]] = i
+	}
+	return bld(preorder, iIdx, 0, len(preorder), 0, len(preorder))
+}
+
+var _ = buildTree