Merge pull request #589 from 0xff-dev/865

Add solution and test-cases for problem 865

leetcode/801-900/0865.Smallest-Subtree-with-all-the-Deepest-Nodes/README.md

@@ -1,28 +1,41 @@
 # [865.Smallest Subtree with all the Deepest Nodes][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 the `root` of a binary tree, the depth of each node is **the shortest distance to the root**.
+
+Return the smallest subtree such that it contains **all the deepest nodes** in the original tree.
+
+A node is called **the deepest** if it has the largest depth possible among any node in the entire tree.
+
+The **subtree** of a node is a tree consisting of that node, plus the set of all descendants of that node.
+
+**Example 1:**  
 
-**Example 1:**
+![example1](./sketch1.png)
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: root = [3,5,1,6,2,0,8,null,null,7,4]
+Output: [2,7,4]
+Explanation: We return the node with value 2, colored in yellow in the diagram.
+The nodes coloured in blue are the deepest nodes of the tree.
+Notice that nodes 5, 3 and 2 contain the deepest nodes in the tree but node 2 is the smallest subtree among them, so we return it.
 ```
 
-## 题意
-> ...
+**Example 2:**
 
-## 题解
-
-### 思路1
-> ...
-Smallest Subtree with all the Deepest Nodes
-```go
 ```
+Input: root = [1]
+Output: [1]
+Explanation: The root is the deepest node in the tree.
+```
+
+**Example 3:**
 
+```
+Input: root = [0,1,3,null,2]
+Output: [2]
+Explanation: The deepest node in the tree is 2, the valid subtrees are the subtrees of nodes 2, 1 and 0 but the subtree of node 2 is the smallest.
+```
 
 ## 结语
 

leetcode/801-900/0865.Smallest-Subtree-with-all-the-Deepest-Nodes/Solution.go

@@ -1,5 +1,56 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+type TreeNode struct {
+	Val         int
+	Left, Right *TreeNode
+}
+
+func Solution(root *TreeNode) *TreeNode {
+	var dfs func(*TreeNode, int)
+	maxDep := 0
+	targetLeafNodes := 0
+	nodeDep := make(map[int]int)
+	dfs = func(now *TreeNode, dep int) {
+		if now == nil {
+			return
+		}
+		nodeDep[now.Val] = dep
+		if now.Left == nil && now.Right == nil {
+			if dep > maxDep {
+				maxDep = dep
+				targetLeafNodes = 1
+			} else if dep == maxDep {
+				targetLeafNodes++
+			}
+			return
+		}
+		dfs(now.Left, dep+1)
+		dfs(now.Right, dep+1)
+	}
+	dfs(root, 1)
+
+	var ans *TreeNode
+	var dfs1 func(*TreeNode) int
+	dfs1 = func(now *TreeNode) int {
+		if now == nil {
+			return 0
+		}
+		left := dfs1(now.Left)
+		right := dfs1(now.Right)
+
+		addOne := 0
+		if nodeDep[now.Val] == maxDep {
+			addOne = 1
+		}
+		r := left + right + addOne
+		if r == targetLeafNodes {
+			if ans == nil || nodeDep[ans.Val] < nodeDep[now.Val] {
+				ans = now
+			}
+		}
+		return r
+	}
+	dfs1(root)
+
+	return ans
 }

leetcode/801-900/0865.Smallest-Subtree-with-all-the-Deepest-Nodes/Solution_test.go

@@ -10,30 +10,55 @@ 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: 3,
+			Left: &TreeNode{
+				Val: 5,
+				Left: &TreeNode{
+					Val: 6,
+				},
+				Right: &TreeNode{
+					Val:   2,
+					Left:  &TreeNode{Val: 7},
+					Right: &TreeNode{Val: 4},
+				},
+			},
+			Right: &TreeNode{
+				Val:   1,
+				Left:  &TreeNode{Val: 0},
+				Right: &TreeNode{Val: 8},
+			},
+		}, 2},
+		{"TestCase2", &TreeNode{Val: 1}, 1},
+		{"TestCase3", &TreeNode{
+			Val: 0,
+			Left: &TreeNode{
+				Val:   1,
+				Right: &TreeNode{Val: 2},
+			},
+			Right: &TreeNode{Val: 3},
+		}, 2},
 	}
 
 	//	开始测试
 	for i, c := range cases {
 		t.Run(c.name+" "+strconv.Itoa(i), func(t *testing.T) {
 			got := Solution(c.inputs)
-			if !reflect.DeepEqual(got, c.expect) {
+			if !reflect.DeepEqual(got.Val, c.expect) {
 				t.Fatalf("expected: %v, but got: %v, with inputs: %v",
 					c.expect, got, c.inputs)
 			}
 		})
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }