Merge pull request #108 from vaskoz/day49

Day49

README.md

@@ -60,3 +60,4 @@ problems from
 * [Day 45](https://github.com/vaskoz/dailycodingproblem-go/issues/101)
 * [Day 46](https://github.com/vaskoz/dailycodingproblem-go/issues/103)
 * [Day 47](https://github.com/vaskoz/dailycodingproblem-go/issues/105)
+* [Day 49](https://github.com/vaskoz/dailycodingproblem-go/issues/107)

day49/problem.go

@@ -0,0 +1,20 @@
+package day49
+
+// MaxSubArray returns the maximum possible sum of a contiguous sub-array.
+// Runs in O(N) time and O(1) space.
+func MaxSubArray(arr []int) int {
+	var maxEndingHere, maxSoFar int
+	for i := range arr {
+		maxEndingHere = max(arr[i], maxEndingHere+arr[i])
+		maxSoFar = max(maxSoFar, maxEndingHere)
+	}
+	return maxSoFar
+}
+
+// max returns the larger of two ints.
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}

day49/problem_test.go

@@ -0,0 +1,28 @@
+package day49
+
+import "testing"
+
+var testcases = []struct {
+	arr    []int
+	maxSum int
+}{
+	{[]int{34, -50, 42, 14, -5, 86}, 137},
+	{[]int{-5, -1, -8, -9}, 0},
+}
+
+func TestMaxSubArray(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := MaxSubArray(tc.arr); result != tc.maxSum {
+			t.Errorf("Expected %d got %d", tc.maxSum, result)
+		}
+	}
+}
+
+func BenchmarkMaxSubArray(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			MaxSubArray(tc.arr)
+		}
+	}
+}