Day117

README.md

@@ -126,6 +126,7 @@ problems from
 * [Day 114](https://github.com/vaskoz/dailycodingproblem-go/issues/237)
 * [Day 115](https://github.com/vaskoz/dailycodingproblem-go/issues/238)
 * [Day 116](https://github.com/vaskoz/dailycodingproblem-go/issues/242)
+* [Day 117](https://github.com/vaskoz/dailycodingproblem-go/issues/245)
 * [Day 118](https://github.com/vaskoz/dailycodingproblem-go/issues/246)
 * [Day 120](https://github.com/vaskoz/dailycodingproblem-go/issues/248)
 * [Day 122](https://github.com/vaskoz/dailycodingproblem-go/issues/252)

day117/problem.go

@@ -0,0 +1,41 @@
+package day117
+
+// BinaryTree is a binary tree of integers.
+type BinaryTree struct {
+	Value       int
+	Left, Right *BinaryTree
+}
+
+// MinimumSumLevel returns both the 1-based level and sum of that level.
+// Runs in O(N) time and O(1) extra space.
+// If you pass in "nil", the sum is 0 and the level is 0.
+func MinimumSumLevel(tree *BinaryTree) (minSum int, minLevel int) {
+	if tree == nil {
+		return
+	}
+	minSum = int(^uint(0) >> 1)
+	minLevel = minSum
+	current := make([]*BinaryTree, 0, 1)
+	current = append(current, tree)
+	level := 1
+	for len(current) != 0 {
+		nextLevel := make([]*BinaryTree, 0, 2*cap(current))
+		var sum int
+		for _, ptr := range current {
+			sum += ptr.Value
+			if ptr.Left != nil {
+				nextLevel = append(nextLevel, ptr.Left)
+			}
+			if ptr.Right != nil {
+				nextLevel = append(nextLevel, ptr.Right)
+			}
+		}
+		if sum < minSum {
+			minSum = sum
+			minLevel = level
+		}
+		level++
+		current = nextLevel
+	}
+	return
+}

day117/problem_test.go

@@ -0,0 +1,65 @@
+package day117
+
+import "testing"
+
+var testcases = []struct {
+	tree             *BinaryTree
+	minLevel, minSum int
+}{
+	{nil, 0, 0},
+	{&BinaryTree{5,
+		&BinaryTree{10, nil, nil},
+		&BinaryTree{20, nil, nil}},
+		1,
+		5},
+	{&BinaryTree{5,
+		&BinaryTree{10, nil, nil},
+		&BinaryTree{-20, nil, nil}},
+		2,
+		-10},
+	{&BinaryTree{5,
+		&BinaryTree{10,
+			&BinaryTree{30,
+				nil,
+				&BinaryTree{0,
+					&BinaryTree{-7, nil, nil},
+					&BinaryTree{-9, nil, nil}}},
+			nil},
+		&BinaryTree{20,
+			nil,
+			&BinaryTree{0,
+				&BinaryTree{3, nil, nil},
+				&BinaryTree{5, nil, nil}}}},
+		5,
+		-16},
+	{&BinaryTree{5,
+		&BinaryTree{10,
+			&BinaryTree{30,
+				nil,
+				&BinaryTree{-9, nil, nil}},
+			nil},
+		&BinaryTree{20,
+			nil,
+			&BinaryTree{0,
+				&BinaryTree{3, nil, nil},
+				&BinaryTree{5, nil, nil}}}},
+		4,
+		-1},
+}
+
+func TestMinimumSumLevel(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if sum, level := MinimumSumLevel(tc.tree); sum != tc.minSum && level != tc.minLevel {
+			t.Errorf("Expected (%d,%d), but got (%d,%d)", tc.minSum, tc.minLevel, sum, level)
+		}
+	}
+}
+
+func BenchmarkMinimumSumLevel(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			MinimumSumLevel(tc.tree)
+		}
+	}
+}