feat: add golang solution to lcci problems: No. 04.04, 04.05

Author: maolonglong

lcci/04.04.Check Balance/README.md

@@ -72,6 +72,42 @@ class Solution {
 }
 ```
 
+### **Go**
+
+自底向上递归
+
+```go
+func isBalanced(root *TreeNode) bool {
+	return depth(root) >= 0
+}
+
+func depth(root *TreeNode) int {
+	if root == nil {
+		return 0
+	}
+	left := depth(root.Left)
+	right := depth(root.Right)
+	if left == -1 || right == -1 || abs(left-right) > 1 {
+		return -1
+	}
+	return max(left, right) + 1
+}
+
+func max(x, y int) int {
+	if x > y {
+		return x
+	}
+	return y
+}
+
+func abs(x int) int {
+	if x < 0 {
+		return -x
+	}
+	return x
+}
+```
+
 ### **...**
 
 ```

lcci/04.04.Check Balance/README_EN.md

@@ -107,6 +107,42 @@ class Solution {
 }
 ```
 
+### **Go**
+
+Bottom-up recursion
+
+```go
+func isBalanced(root *TreeNode) bool {
+	return depth(root) >= 0
+}
+
+func depth(root *TreeNode) int {
+	if root == nil {
+		return 0
+	}
+	left := depth(root.Left)
+	right := depth(root.Right)
+	if left == -1 || right == -1 || abs(left-right) > 1 {
+		return -1
+	}
+	return max(left, right) + 1
+}
+
+func max(x, y int) int {
+	if x > y {
+		return x
+	}
+	return y
+}
+
+func abs(x int) int {
+	if x < 0 {
+		return -x
+	}
+	return x
+}
+```
+
 ### **...**
 
 ```

lcci/04.04.Check Balance/Solution.go

@@ -0,0 +1,29 @@
+func isBalanced(root *TreeNode) bool {
+	return depth(root) >= 0
+}
+
+func depth(root *TreeNode) int {
+	if root == nil {
+		return 0
+	}
+	left := depth(root.Left)
+	right := depth(root.Right)
+	if left == -1 || right == -1 || abs(left-right) > 1 {
+		return -1
+	}
+	return max(left, right) + 1
+}
+
+func max(x, y int) int {
+	if x > y {
+		return x
+	}
+	return y
+}
+
+func abs(x int) int {
+	if x < 0 {
+		return -x
+	}
+	return x
+}

lcci/04.05.Legal Binary Search Tree/README.md

@@ -83,6 +83,51 @@ class Solution {
 }
 ```
 
+### **Go**
+
+- 非递归中序遍历
+
+```go
+func isValidBST(root *TreeNode) bool {
+	stack := make([]*TreeNode, 0)
+	var prev *TreeNode = nil
+	node := root
+	for len(stack) > 0 || node != nil {
+		for node != nil {
+			stack = append(stack, node)
+			node = node.Left
+		}
+		node = stack[len(stack)-1]
+		stack = stack[:len(stack)-1]
+		if prev == nil || node.Val > prev.Val {
+			prev = node
+		} else {
+			return false
+		}
+		node = node.Right
+	}
+	return true
+}
+```
+
+- 利用上界下界判定
+
+```go
+func isValidBST(root *TreeNode) bool {
+	return check(root, math.MinInt64, math.MaxInt64)
+}
+
+func check(node *TreeNode, lower, upper int) bool {
+	if node == nil {
+		return true
+	}
+	if node.Val <= lower || node.Val >= upper {
+		return false
+	}
+	return check(node.Left, lower, node.Val) && check(node.Right, node.Val, upper)
+}
+```
+
 ### **...**
 
 ```

lcci/04.05.Legal Binary Search Tree/README_EN.md

@@ -112,6 +112,51 @@ class Solution {
 }
 ```
 
+### **Go**
+
+- Non-recursive in-order traversal
+
+```go
+func isValidBST(root *TreeNode) bool {
+	stack := make([]*TreeNode, 0)
+	var prev *TreeNode = nil
+	node := root
+	for len(stack) > 0 || node != nil {
+		for node != nil {
+			stack = append(stack, node)
+			node = node.Left
+		}
+		node = stack[len(stack)-1]
+		stack = stack[:len(stack)-1]
+		if prev == nil || node.Val > prev.Val {
+			prev = node
+		} else {
+			return false
+		}
+		node = node.Right
+	}
+	return true
+}
+```
+
+- Use upper bound and lower bound to check
+
+```go
+func isValidBST(root *TreeNode) bool {
+	return check(root, math.MinInt64, math.MaxInt64)
+}
+
+func check(node *TreeNode, lower, upper int) bool {
+	if node == nil {
+		return true
+	}
+	if node.Val <= lower || node.Val >= upper {
+		return false
+	}
+	return check(node.Left, lower, node.Val) && check(node.Right, node.Val, upper)
+}
+```
+
 ### **...**
 
 ```

lcci/04.05.Legal Binary Search Tree/Solution.go

@@ -0,0 +1,34 @@
+func isValidBST(root *TreeNode) bool {
+	return check(root, math.MinInt64, math.MaxInt64)
+}
+
+func check(node *TreeNode, lower, upper int) bool {
+	if node == nil {
+		return true
+	}
+	if node.Val <= lower || node.Val >= upper {
+		return false
+	}
+	return check(node.Left, lower, node.Val) && check(node.Right, node.Val, upper)
+}
+
+// func isValidBST(root *TreeNode) bool {
+// 	stack := make([]*TreeNode, 0)
+// 	var prev *TreeNode = nil
+// 	node := root
+// 	for len(stack) > 0 || node != nil {
+// 		for node != nil {
+// 			stack = append(stack, node)
+// 			node = node.Left
+// 		}
+// 		node = stack[len(stack)-1]
+// 		stack = stack[:len(stack)-1]
+// 		if prev == nil || node.Val > prev.Val {
+// 			prev = node
+// 		} else {
+// 			return false
+// 		}
+// 		node = node.Right
+// 	}
+// 	return true
+// }