From 34296986a15b1db663d931d5ea032bcbd63b5841 Mon Sep 17 00:00:00 2001
From: Vasko Zdravevski <vaskoz@users.noreply.github.com>
Date: Fri, 12 Apr 2019 10:10:13 -0600
Subject: [PATCH 1/3] day 233: simple fibonacci O(n) time and O(1) space

---
 day233/problem.go      | 13 +++++++++++++
 day233/problem_test.go | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+)
 create mode 100644 day233/problem.go
 create mode 100644 day233/problem_test.go

diff --git a/day233/problem.go b/day233/problem.go
new file mode 100644
index 0000000..b002c65
--- /dev/null
+++ b/day233/problem.go
@@ -0,0 +1,13 @@
+package day233
+
+// FastFibonnaci runs in O(N) time with O(1) space.
+func FastFibonnaci(n uint) uint {
+	if n < 2 {
+		return n
+	}
+	first, second := uint(0), uint(1)
+	for i := uint(1); i < n; i++ {
+		first, second = second, first+second
+	}
+	return second
+}
diff --git a/day233/problem_test.go b/day233/problem_test.go
new file mode 100644
index 0000000..40e051a
--- /dev/null
+++ b/day233/problem_test.go
@@ -0,0 +1,32 @@
+package day233
+
+import "testing"
+
+var testcases = []struct {
+	n, fib uint
+}{
+	{0, 0},
+	{1, 1},
+	{2, 1},
+	{12, 144},
+	{28, 317811},
+	{44, 701408733},
+	{87, 679891637638612258},
+}
+
+func TestFastFibonnaci(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := FastFibonnaci(tc.n); result != tc.fib {
+			t.Errorf("Given n=%d, expected %d, got %d", tc.n, tc.fib, result)
+		}
+	}
+}
+
+func BenchmarkFastFibonnaci(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			FastFibonnaci(tc.n)
+		}
+	}
+}

From 022432a81b2be50cb5493bfefd0578fe749b4d59 Mon Sep 17 00:00:00 2001
From: Vasko Zdravevski <vaskoz@users.noreply.github.com>
Date: Fri, 12 Apr 2019 10:10:40 -0600
Subject: [PATCH 2/3] add day 233 to readme

---
 README.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/README.md b/README.md
index 05a4d52..72fdbc9 100644
--- a/README.md
+++ b/README.md
@@ -241,3 +241,4 @@ problems from
 * [Day 230](https://github.com/vaskoz/dailycodingproblem-go/issues/473)
 * [Day 231](https://github.com/vaskoz/dailycodingproblem-go/issues/475)
 * [Day 232](https://github.com/vaskoz/dailycodingproblem-go/issues/477)
+* [Day 233](https://github.com/vaskoz/dailycodingproblem-go/issues/479)

From ded312742ab17372f46109f376d6921e2c635245 Mon Sep 17 00:00:00 2001
From: Vasko Zdravevski <vaskoz@users.noreply.github.com>
Date: Fri, 12 Apr 2019 10:15:36 -0600
Subject: [PATCH 3/3] day 233: add overflow detection

---
 day233/problem.go      | 20 +++++++++++++++++---
 day233/problem_test.go | 22 ++++++++++++----------
 2 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/day233/problem.go b/day233/problem.go
index b002c65..528e223 100644
--- a/day233/problem.go
+++ b/day233/problem.go
@@ -1,13 +1,27 @@
 package day233
 
+import "errors"
+
+var errOverflow = errors.New("overflow occurred")
+
+// ErrOverflow represents an overflow error.
+func ErrOverflow() error {
+	return errOverflow
+}
+
 // FastFibonnaci runs in O(N) time with O(1) space.
-func FastFibonnaci(n uint) uint {
+// Returns an error if overflow occurs.
+func FastFibonnaci(n uint) (uint, error) {
 	if n < 2 {
-		return n
+		return n, nil
 	}
 	first, second := uint(0), uint(1)
+	var err error
 	for i := uint(1); i < n; i++ {
 		first, second = second, first+second
+		if second < first {
+			return 0, errOverflow
+		}
 	}
-	return second
+	return second, err
 }
diff --git a/day233/problem_test.go b/day233/problem_test.go
index 40e051a..9d05d0f 100644
--- a/day233/problem_test.go
+++ b/day233/problem_test.go
@@ -4,21 +4,23 @@ import "testing"
 
 var testcases = []struct {
 	n, fib uint
+	err    error
 }{
-	{0, 0},
-	{1, 1},
-	{2, 1},
-	{12, 144},
-	{28, 317811},
-	{44, 701408733},
-	{87, 679891637638612258},
+	{0, 0, nil},
+	{1, 1, nil},
+	{2, 1, nil},
+	{12, 144, nil},
+	{28, 317811, nil},
+	{44, 701408733, nil},
+	{87, 679891637638612258, nil},
+	{100, 0, ErrOverflow()},
 }
 
 func TestFastFibonnaci(t *testing.T) {
 	t.Parallel()
 	for _, tc := range testcases {
-		if result := FastFibonnaci(tc.n); result != tc.fib {
-			t.Errorf("Given n=%d, expected %d, got %d", tc.n, tc.fib, result)
+		if result, err := FastFibonnaci(tc.n); result != tc.fib || err != tc.err {
+			t.Errorf("Given n=%d, expected (%d,%v), got (%d,%v)", tc.n, tc.fib, tc.err, result, err)
 		}
 	}
 }
@@ -26,7 +28,7 @@ func TestFastFibonnaci(t *testing.T) {
 func BenchmarkFastFibonnaci(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		for _, tc := range testcases {
-			FastFibonnaci(tc.n)
+			FastFibonnaci(tc.n) //nolint
 		}
 	}
 }