add new solutions

solutions/0/q98/solution.go

@@ -0,0 +1,39 @@
+package q98
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func isValid(node *TreeNode) (bool, int, int) {
+	if node.Left == nil && node.Right == nil {
+		return true, node.Val, node.Val
+	}
+
+	minv, maxv := node.Val, node.Val
+
+	if node.Left != nil {
+		valid, lmin, lmax := isValid(node.Left)
+		if !valid || lmax >= node.Val {
+			return false, 0, 0
+		}
+		minv = lmin
+	}
+	if node.Right != nil {
+		valid, rmin, rmax := isValid(node.Right)
+		if !valid || rmin <= node.Val {
+			return false, 0, 0
+		}
+		maxv = rmax
+	}
+
+	return true, minv, maxv
+}
+
+func isValidBST(root *TreeNode) bool {
+	valid, _, _ := isValid(root)
+	return valid
+}
+
+var _ = isValidBST