Repository: vaskoz/dailycodingproblem-go (go)

Issue:
Day 102
Good morning! Here's your coding interview problem for today.

This problem was asked by Lyft.

Given a list of integers and a number K, return which contiguous elements of the list sum to K.

For example, if the list is `[1, 2, 3, 4, 5]` and K is `9`, then it should return `[2, 3, 4]`.

Pull request:
Day102
Resolves #214.

Patch:
diff --git a/README.md b/README.md
index 231ca71..cb56aaf 100644
--- a/README.md
+++ b/README.md
@@ -111,3 +111,4 @@ problems from
 * [Day 99](https://github.com/vaskoz/dailycodingproblem-go/issues/205)
 * [Day 100](https://github.com/vaskoz/dailycodingproblem-go/issues/209)
 * [Day 101](https://github.com/vaskoz/dailycodingproblem-go/issues/212)
+* [Day 102](https://github.com/vaskoz/dailycodingproblem-go/issues/214)
diff --git a/day102/problem.go b/day102/problem.go
new file mode 100644
index 0000000..87170ba
--- /dev/null
+++ b/day102/problem.go
@@ -0,0 +1,39 @@
+package day102
+
+// ContiguousSumBrute uses brute-force to return the
+// contiguous subset that sums to K.
+// Runtime is O(N^2) and O(1) space.
+func ContiguousSumBrute(nums []int, k int) []int {
+	var result []int
+	for i := range nums {
+		var sum int
+		for j := i; j < len(nums); j++ {
+			sum += nums[j]
+			if sum == k {
+				return nums[i : j+1]
+			}
+		}
+	}
+	return result
+}
+
+// ContiguousSumFaster uses a window to return the
+// contiguous subset that sums to K.
+// Runtime is O(N) and O(1) space.
+func ContiguousSumFaster(nums []int, k int) []int {
+	var result []int
+	var sum, begin int
+	for end := 0; end < len(nums); end++ {
+		sum += nums[end]
+		if sum == k {
+			result = nums[begin : end+1]
+			break
+		} else if sum > k {
+			sum -= nums[begin]
+			sum -= nums[end]
+			begin++
+			end--
+		}
+	}
+	return result
+}


Test patch:
diff --git a/day102/problem_test.go b/day102/problem_test.go
new file mode 100644
index 0000000..f973aaf
--- /dev/null
+++ b/day102/problem_test.go
@@ -0,0 +1,53 @@
+package day102
+
+import (
+	"reflect"
+	"testing"
+)
+
+var testcases = []struct {
+	input    []int
+	k        int
+	expected []int
+}{
+	{[]int{1, 2, 3, 4, 5}, 9, []int{2, 3, 4}},
+	{[]int{1, 2, 3, 4, 5}, 16, nil},
+	{[]int{1, 2, 3, 4, 5}, 15, []int{1, 2, 3, 4, 5}},
+	{[]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
+		15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25},
+		49, []int{4, 5, 6, 7, 8, 9, 10}},
+}
+
+func TestContiguousSumBrute(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := ContiguousSumBrute(tc.input, tc.k); !reflect.DeepEqual(tc.expected, result) {
+			t.Errorf("Expected %v got %v", tc.expected, result)
+		}
+	}
+}
+
+func BenchmarkContiguousSumBrute(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			ContiguousSumBrute(tc.input, tc.k)
+		}
+	}
+}
+
+func TestContiguousSumFaster(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := ContiguousSumFaster(tc.input, tc.k); !reflect.DeepEqual(tc.expected, result) {
+			t.Errorf("Expected %v got %v", tc.expected, result)
+		}
+	}
+}
+
+func BenchmarkContiguousSumFaster(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			ContiguousSumFaster(tc.input, tc.k)
+		}
+	}
+}