124 ut pass

Author: aQua

Algorithms/0124.binary-tree-maximum-path-sum/binary-tree-maximum-path-sum.go

@@ -3,25 +3,49 @@ package Problem0124
 import (
 	"github.com/aQuaYi/LeetCode-in-Golang/kit"
 )
+
 type TreeNode = kit.TreeNode
 
 func maxPathSum(root *TreeNode) int {
-	res := -1<<31
-if root == nil {
-	return res 
-}
+	if root == nil {
+		return -1<<31 
+	}
 
+	sum := root.Val +
+		max(0, maxSince(root.Left)) +
+		max(0, maxSince(root.Right))
 
-	return  res 
+	return max(sum,
+		max(maxPathSum(root.Left), maxPathSum(root.Right)))
 }
 
-func maxRoot2Leaf() {
-	
+// 返回，从 root 出发，包含 root 在内的所有可能路径的最大的 sum 值
+func maxSince(root *TreeNode) int {
+	res := -1 << 31
+
+	var dfs func(*TreeNode, int)
+	dfs = func(root *TreeNode, sum int) {
+		if root == nil {
+			return
+		}
+
+		sum += root.Val
+		if res < sum {
+			res = sum
+		}
+
+		dfs(root.Left, sum)
+		dfs(root.Right, sum)
+	}
+
+	dfs(root, 0)
+
+	return res
 }
 
-func max(a, b int ) int  {
-	if a> b {
-		return a 
+func max(a, b int) int {
+	if a > b {
+		return a
 	}
-	return b 
-}
+	return b
+}

Algorithms/0124.binary-tree-maximum-path-sum/binary-tree-maximum-path-sum_test.go

@@ -18,6 +18,12 @@ func Test_Problem0124(t *testing.T) {
 		ans     int
 	}{
 
+		{
+			[]int{-10, 100, -1, -2},
+			[]int{-10, -1, 100, -2},
+			100,
+		},
+
 		{
 			[]int{10, 10, -1, -2},
 			[]int{10, -1, 10, -2},