Merge 5e0cd11 into 88461c6

README.md

@@ -173,3 +173,4 @@ problems from
 * [Day 161](https://github.com/vaskoz/dailycodingproblem-go/issues/334)
 * [Day 162](https://github.com/vaskoz/dailycodingproblem-go/issues/335)
 * [Day 163](https://github.com/vaskoz/dailycodingproblem-go/issues/336)
+* [Day 164](https://github.com/vaskoz/dailycodingproblem-go/issues/340)

day164/problem.go

@@ -0,0 +1,17 @@
+package day164
+
+// FindDuplicate returns the one duplicate value between
+// 1 to N.
+// Assumes N+1 values are provided.
+func FindDuplicate(nums []int) int {
+	sub := len(nums) - 1
+	sum := 0
+	for _, n := range nums {
+		sum += n
+		for sum > 0 && sub > 0 {
+			sum -= sub
+			sub--
+		}
+	}
+	return sum
+}

day164/problem_test.go

@@ -0,0 +1,27 @@
+package day164
+
+import "testing"
+
+var testcases = []struct {
+	nums []int
+	dup  int
+}{
+	{[]int{3, 1, 5, 4, 2, 4}, 4},
+}
+
+func TestFindDuplicate(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if dup := FindDuplicate(tc.nums); dup != tc.dup {
+			t.Errorf("Expected %v got %v", tc.dup, dup)
+		}
+	}
+}
+
+func BenchmarkFindDuplicate(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			FindDuplicate(tc.nums)
+		}
+	}
+}