Merge pull request #859 from 0xff-dev/671

Add solution and test-cases for problem 671

Author: 6boris

leetcode/601-700/0671.Second-Minimum-Node-In-a-Binary-Tree/README.md

@@ -1,28 +1,31 @@
 # [671.Second Minimum Node In a Binary Tree][title]
 
-> [!WARNING|style:flat]
-> This question is temporarily unanswered if you have good ideas. Welcome to [Create Pull Request PR](https://github.com/kylesliu/awesome-golang-algorithm)
-
 ## Description
+Given a non-empty special binary tree consisting of nodes with the non-negative value, where each node in this tree has exactly `two` or `zero` sub-node. If the node has two sub-nodes, then this node's value is the smaller value among its two sub-nodes. More formally, the property `root.val = min(root.left.val, root.right.val)` always holds.
+
+Given such a binary tree, you need to output the **second minimum** value in the set made of all the nodes' value in the whole tree.
+
+If no such second minimum value exists, output -1 instead.
 
-**Example 1:**
+**Example 1:**  
+
+![1](./smbt1.jpeg)
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: root = [2,2,5,null,null,5,7]
+Output: 5
+Explanation: The smallest value is 2, the second smallest value is 5.
 ```
 
-## 题意
-> ...
+**Example 2:**  
 
-## 题解
+![2](./smbt2.jpeg)
 
-### 思路1
-> ...
-Second Minimum Node In a Binary Tree
-```go
 ```
-
+Input: root = [2,2,2]
+Output: -1
+Explanation: The smallest value is 2, but there isn't any second smallest value.
+```
 
 ## 结语
 

leetcode/601-700/0671.Second-Minimum-Node-In-a-Binary-Tree/Solution.go

@@ -1,5 +1,37 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+import "sort"
+
+type TreeNode struct {
+	Val         int
+	Left, Right *TreeNode
+}
+
+// 不是最好的解法
+func Solution(root *TreeNode) int {
+	queue := []*TreeNode{root}
+	v := make([]int, 0)
+	uv := map[int]struct{}{}
+
+	for len(queue) > 0 {
+		nq := make([]*TreeNode, 0)
+		for _, cur := range queue {
+			if _, ok := uv[cur.Val]; !ok {
+				v = append(v, cur.Val)
+				uv[cur.Val] = struct{}{}
+			}
+			if cur.Left != nil {
+				nq = append(nq, cur.Left)
+			}
+			if cur.Right != nil {
+				nq = append(nq, cur.Right)
+			}
+		}
+		queue = nq
+	}
+	sort.Ints(v)
+	if len(v) < 2 {
+		return -1
+	}
+	return v[1]
 }

leetcode/601-700/0671.Second-Minimum-Node-In-a-Binary-Tree/Solution_test.go

@@ -10,12 +10,23 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
-		expect bool
+		inputs *TreeNode
+		expect int
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", &TreeNode{
+			Val:  2,
+			Left: &TreeNode{Val: 2},
+			Right: &TreeNode{
+				Val:   5,
+				Left:  &TreeNode{Val: 5},
+				Right: &TreeNode{Val: 7},
+			},
+		}, 5},
+		{"TestCase", &TreeNode{
+			Val:   2,
+			Left:  &TreeNode{Val: 2},
+			Right: &TreeNode{Val: 2},
+		}, -1},
 	}
 
 	//	开始测试
@@ -30,10 +41,10 @@ func TestSolution(t *testing.T) {
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }