Merge pull request #202 from vaskoz/day94

Day94

README.md

@@ -102,5 +102,6 @@ problems from
 * [Day 90](https://github.com/vaskoz/dailycodingproblem-go/issues/189)
 * [Day 91](https://github.com/vaskoz/dailycodingproblem-go/issues/192)
 * [Day 92](https://github.com/vaskoz/dailycodingproblem-go/issues/194)
+* [Day 94](https://github.com/vaskoz/dailycodingproblem-go/issues/197)
 * [Day 95](https://github.com/vaskoz/dailycodingproblem-go/issues/198)
 * [Day 96](https://github.com/vaskoz/dailycodingproblem-go/issues/200)

day94/problem.go

@@ -0,0 +1,41 @@
+package day94
+
+// BinaryTree is a binary tree with an integer value.
+type BinaryTree struct {
+	Value       int
+	Left, Right *BinaryTree
+}
+
+// MaxPathSum returns the maximum path sum in a given
+// binary tree.
+func MaxPathSum(tree *BinaryTree) int {
+	const MinInt = -int(^uint(0)>>1) - 1
+	result := MinInt
+	maxPathSum(tree, &result)
+	return result
+}
+
+func maxPathSum(node *BinaryTree, res *int) int {
+	if node == nil {
+		return 0
+	} else if node.Left == nil && node.Right == nil {
+		return node.Value
+	}
+	leftSum := maxPathSum(node.Left, res)
+	rightSum := maxPathSum(node.Right, res)
+	if node.Left != nil && node.Right != nil {
+		*res = max(*res, leftSum+rightSum+node.Value)
+		return max(leftSum, rightSum) + node.Value
+	}
+	if node.Left == nil {
+		return rightSum + node.Value
+	}
+	return leftSum + node.Value
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}

day94/problem_test.go

@@ -0,0 +1,35 @@
+package day94
+
+import "testing"
+
+var tree = &BinaryTree{
+	-15,
+	&BinaryTree{5,
+		&BinaryTree{-8,
+			&BinaryTree{2, nil, nil},
+			&BinaryTree{6, nil, nil}},
+		&BinaryTree{1, nil, nil}},
+	&BinaryTree{6,
+		&BinaryTree{3, nil, nil},
+		&BinaryTree{9, nil,
+			&BinaryTree{0,
+				&BinaryTree{4, nil, nil},
+				&BinaryTree{-1, &BinaryTree{10, nil, nil}, nil},
+			},
+		},
+	},
+}
+
+func TestMaxPathSum(t *testing.T) {
+	t.Parallel()
+	result := MaxPathSum(tree)
+	if result != 27 {
+		t.Errorf("Expected 27 got %v", result)
+	}
+}
+
+func BenchmarkMaxPathSum(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		MaxPathSum(tree)
+	}
+}