binary_tree_maximum_path_sum

Author: hitzzc

README.md

@@ -107,6 +107,7 @@ Golang solution for leetcode. For each problem, there is a simple *_test.go to t
 #### [118. pascal's triangle](https://github.com/hitzzc/go-leetcode/tree/master/pascals_triangle)
 #### [119. pascal's triangle II](https://github.com/hitzzc/go-leetcode/tree/master/pascals_triangle_II)
 #### [120. triangle](https://github.com/hitzzc/go-leetcode/tree/master/triangle)
+#### [124. binary tree maximum path sum](https://github.com/hitzzc/go-leetcode/tree/master/binary_tree_maximum_path_sum)
 #### [125. valid palindrome](https://github.com/hitzzc/go-leetcode/tree/master/valid_palindrome)
 
 

binary_tree_maximum_path_sum/binary_tree_maximum_path_sum.go

@@ -0,0 +1,45 @@
+package binary_tree_maximum_path_sum
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+type solution struct {
+	max   int
+	first bool
+}
+
+func maxPathSum(root *TreeNode) int {
+	s := &solution{first: true}
+	s.helper(root)
+	return s.max
+}
+
+func (this *solution) helper(root *TreeNode) (max int) {
+	if root == nil {
+		return 0
+	}
+	tmp := root.Val
+	left := this.helper(root.Left)
+	if left > 0 {
+		tmp += left
+	}
+	right := this.helper(root.Right)
+	if right > 0 {
+		tmp += right
+	}
+	if this.first || tmp > this.max {
+		this.first = false
+		this.max = tmp
+	}
+	if left > 0 && left > right {
+		max = root.Val + left
+	} else if right > 0 && right > left {
+		max = root.Val + right
+	} else {
+		max = root.Val
+	}
+	return
+}