Merge pull request #88 from vaskoz/day40

Day40

README.md

@@ -50,3 +50,4 @@ problems from
 * [Day 36](https://github.com/vaskoz/dailycodingproblem-go/issues/79)
 * [Day 37](https://github.com/vaskoz/dailycodingproblem-go/issues/81)
 * [Day 38](https://github.com/vaskoz/dailycodingproblem-go/issues/83)
+* [Day 40](https://github.com/vaskoz/dailycodingproblem-go/issues/87)

day40/problem.go

@@ -0,0 +1,33 @@
+package day40
+
+// FindOnce returns the number that appears only once in a list where
+// other numbers appear 3 times.
+// Runs in O(N) time and O(1) space.
+func FindOnce(nums []int) int {
+	var ones, twos int
+	for _, v := range nums {
+		twos |= ones & v
+		ones ^= v
+		not := ^(ones & twos)
+		ones &= not
+		twos &= not
+	}
+	return ones
+}
+
+// FindOnceMap uses a map to find the non-duplicated value.
+// Runs in O(N) and O(N) space
+func FindOnceMap(nums []int) int {
+	counts := make(map[int]int)
+	for _, v := range nums {
+		counts[v]++
+	}
+	var result int
+	for k, v := range counts {
+		if v == 1 {
+			result = k
+			break
+		}
+	}
+	return result
+}

day40/problem_test.go

@@ -0,0 +1,45 @@
+package day40
+
+import "testing"
+
+var testcases = []struct {
+	input    []int
+	expected int
+}{
+	{[]int{6, 1, 3, 3, 3, 6, 6}, 1},
+	{[]int{13, 19, 13, 13}, 19},
+}
+
+func TestFindOnce(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := FindOnce(tc.input); tc.expected != result {
+			t.Errorf("Expected %v got %v", tc.expected, result)
+		}
+	}
+}
+
+func BenchmarkFindOnce(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			FindOnce(tc.input)
+		}
+	}
+}
+
+func TestFindOnceMap(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := FindOnceMap(tc.input); tc.expected != result {
+			t.Errorf("Expected %v got %v", tc.expected, result)
+		}
+	}
+}
+
+func BenchmarkFindOnceMap(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			FindOnceMap(tc.input)
+		}
+	}
+}