u

2026-06-26 01:27:21 +10:00
parent 416b0e9954
commit e2f0b5c11a
2 changed files with 173 additions and 0 deletions
@@ -0,0 +1,104 @@
+package top100liked
+
+// https://leetcode.cn/problems/lowest-common-ancestor-of-a-binary-tree/?envType=study-plan-v2&envId=top-100-liked
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func buildTree(arr []*int) *TreeNode {
+	if len(arr) == 0 || arr[0] == nil {
+		return nil
+	}
+
+	root := &TreeNode{Val: *arr[0]}
+	queue := []*TreeNode{root}
+	i := 1
+
+	for len(queue) > 0 && i < len(arr) {
+		node := queue[0]
+		queue = queue[1:]
+
+		// 处理左孩子
+		if i < len(arr) {
+			if arr[i] != nil {
+				node.Left = &TreeNode{Val: *arr[i]}
+				queue = append(queue, node.Left)
+			}
+			i++
+		}
+
+		// 处理右孩子
+		if i < len(arr) {
+			if arr[i] != nil {
+				node.Right = &TreeNode{Val: *arr[i]}
+				queue = append(queue, node.Right)
+			}
+			i++
+		}
+	}
+
+	return root
+}
+
+// // getParents 包括自身
+// func getParents(root *TreeNode, target int) []*TreeNode {
+// 	parents := []*TreeNode{}
+// 	var res []*TreeNode
+// 	var helper func(root *TreeNode) bool
+// 	helper = func(root *TreeNode) bool {
+// 		if root == nil {
+// 			return false
+// 		}
+// 		if root.Val == target {
+// 			res = append([]*TreeNode{}, parents...)
+// 			res = append(res, root)
+// 			return true
+// 		}
+// 		parents = append(parents, root)
+// 		if helper(root.Left) {
+// 			return true
+// 		}
+// 		if helper(root.Right) {
+// 			return true
+// 		}
+// 		parents = parents[:len(parents)-1]
+// 		return false
+// 	}
+// 	helper(root)
+// 	return res
+// }
+// // 朴素解法，AC，但效率很低
+// func lowestCommonAncestor(root, p, q *TreeNode) *TreeNode {
+// 	p1 := getParents(root, p.Val)
+// 	p2 := getParents(root, q.Val)
+// 	for i := len(p1) - 1; i >= 0; i-- {
+// 		for j := len(p2) - 1; j >= 0; j-- {
+// 			if p1[i].Val == p2[j].Val {
+// 				return p1[i]
+// 			}
+// 		}
+// 	}
+// 	return nil
+// }
+
+func lowestCommonAncestor(root, p, q *TreeNode) *TreeNode {
+	var dfs func(*TreeNode) *TreeNode
+	dfs = func(node *TreeNode) *TreeNode {
+		if node == nil || node == p || node == q {
+			return node
+		}
+		left := dfs(node.Left)
+		right := dfs(node.Right)
+		if left != nil && right != nil {
+			return node
+		}
+		if left != nil {
+			return left
+		}
+		return right
+	}
+	return dfs(root)
+}
@@ -0,0 +1,69 @@
+package top100liked
+
+// https://leetcode.cn/problems/binary-tree-maximum-path-sum/description/?envType=study-plan-v2&envId=top-100-liked
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func buildTree(arr []*int) *TreeNode {
+	if len(arr) == 0 || arr[0] == nil {
+		return nil
+	}
+
+	root := &TreeNode{Val: *arr[0]}
+	queue := []*TreeNode{root}
+	i := 1
+
+	for len(queue) > 0 && i < len(arr) {
+		node := queue[0]
+		queue = queue[1:]
+
+		// 处理左孩子
+		if i < len(arr) {
+			if arr[i] != nil {
+				node.Left = &TreeNode{Val: *arr[i]}
+				queue = append(queue, node.Left)
+			}
+			i++
+		}
+
+		// 处理右孩子
+		if i < len(arr) {
+			if arr[i] != nil {
+				node.Right = &TreeNode{Val: *arr[i]}
+				queue = append(queue, node.Right)
+			}
+			i++
+		}
+	}
+
+	return root
+}
+
+func maxPathSum(root *TreeNode) int {
+	ans := root.Val // TODO: 先随便给个初值, 后面会被更新
+
+	// dfs 返回"从 node 往下单边的最大贡献"
+	var dfs func(node *TreeNode) int
+	dfs = func(node *TreeNode) int {
+		if node == nil {
+			return 0
+		}
+
+		left := max(0, dfs(node.Left))   // 负的就别带
+		right := max(0, dfs(node.Right)) // 负的就别带
+
+		// TODO 1: 在这里转弯的完整路径和, 更新 ans
+		if left+right+node.Val > ans {
+			ans = left + right + node.Val
+		}
+		// TODO 2: 返回往父节点贡献的单边值
+		return max(left, right) + node.Val
+	}
+
+	dfs(root)
+	return ans
+}