规范格式

leetcode/0124.Binary-Tree-Maximum-Path-Sum/124. Binary Tree Maximum Path Sum.go

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+package leetcode
+
+import "math"
+
+import (
+	"github.com/halfrost/LeetCode-Go/structures"
+)
+
+// TreeNode define
+type TreeNode = structures.TreeNode
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+
+func maxPathSum(root *TreeNode) int {
+	if root == nil {
+		return 0
+	}
+	max := math.MinInt32
+	getPathSum(root, &max)
+	return max
+}
+
+func getPathSum(root *TreeNode, maxSum *int) int {
+	if root == nil {
+		return math.MinInt32
+	}
+	left := getPathSum(root.Left, maxSum)
+	right := getPathSum(root.Right, maxSum)
+
+	currMax := max(max(left+root.Val, right+root.Val), root.Val)
+	*maxSum = max(*maxSum, max(currMax, left+right+root.Val))
+	return currMax
+}
+
+func max(a int, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}

leetcode/0124.Binary-Tree-Maximum-Path-Sum/124. Binary Tree Maximum Path Sum_test.go

@@ -0,0 +1,61 @@
+package leetcode
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/halfrost/LeetCode-Go/structures"
+)
+
+type question124 struct {
+	para124
+	ans124
+}
+
+// para 是参数
+// one 代表第一个参数
+type para124 struct {
+	one []int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans124 struct {
+	one int
+}
+
+func Test_Problem124(t *testing.T) {
+
+	qs := []question124{
+
+		question124{
+			para124{[]int{}},
+			ans124{0},
+		},
+
+		question124{
+			para124{[]int{1}},
+			ans124{1},
+		},
+
+		question124{
+			para124{[]int{1, 2, 3}},
+			ans124{6},
+		},
+
+		question124{
+			para124{[]int{-10, 9, 20, structures.NULL, structures.NULL, 15, 7}},
+			ans124{42},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 124------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans124, q.para124
+		fmt.Printf("【input】:%v      ", p)
+		root := structures.Ints2TreeNode(p.one)
+		fmt.Printf("【output】:%v      \n", maxPathSum(root))
+	}
+	fmt.Printf("\n\n\n")
+}

leetcode/0124.Binary-Tree-Maximum-Path-Sum/README.md

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+# [124. Binary Tree Maximum Path Sum](https://leetcode.com/problems/binary-tree-maximum-path-sum/)
+
+
+## 题目
+
+Given a **non-empty** binary tree, find the maximum path sum.
+
+For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The path must contain **at least one node** and does not need to go through the root.
+
+**Example 1:**
+
+    Input: [1,2,3]
+    
+           1
+          / \
+         2   3
+    
+    Output: 6
+
+**Example 2:**
+
+    Input: [-10,9,20,null,null,15,7]
+    
+       -10
+       / \
+      9  20
+        /  \
+       15   7
+    
+    Output: 42
+
+## 题目大意
+
+给定一个非空二叉树，返回其最大路径和。本题中，路径被定义为一条从树中任意节点出发，达到任意节点的序列。该路径至少包含一个节点，且不一定经过根节点。
+
+## 解题思路
+
+- 给出一个二叉树，要求找一条路径使得路径的和是最大的。
+- 这一题思路比较简单，递归维护最大值即可。不过需要比较的对象比较多。`maxPathSum(root) = max(maxPathSum(root.Left), maxPathSum(root.Right), maxPathSumFrom(root.Left) (if>0) + maxPathSumFrom(root.Right) (if>0) + root.Val)` ，其中，`maxPathSumFrom(root) = max(maxPathSumFrom(root.Left), maxPathSumFrom(root.Right)) + root.Val`
+