Day75

README.md

@@ -84,3 +84,4 @@ problems from
 * [Day 72](https://github.com/vaskoz/dailycodingproblem-go/issues/153)
 * [Day 73](https://github.com/vaskoz/dailycodingproblem-go/issues/155)
 * [Day 74](https://github.com/vaskoz/dailycodingproblem-go/issues/157)
+* [Day 75](https://github.com/vaskoz/dailycodingproblem-go/issues/159)

day75/problem.go

@@ -0,0 +1,39 @@
+package day75
+
+// LongestIncreasingSubsequence returns the longest increasing subsequence.
+// Runs in O(N log N) time.
+func LongestIncreasingSubsequence(X []int) []int {
+	p := make([]int, len(X))
+	m := make([]int, len(X)+1)
+	l := 0
+	for i := range X {
+		lo := 1
+		hi := l
+		for lo <= hi {
+			var mid int
+			if (lo+hi)%2 == 0 {
+				mid = (lo + hi) / 2
+			} else {
+				mid = ((lo + hi) / 2) + 1
+			}
+			if X[m[mid]] < X[i] {
+				lo = mid + 1
+			} else {
+				hi = mid - 1
+			}
+		}
+		newL := lo
+		p[i] = m[newL-1]
+		m[newL] = i
+		if newL > l {
+			l = newL
+		}
+	}
+	s := make([]int, l)
+	k := m[l]
+	for i := range s {
+		s[len(s)-1-i] = X[k]
+		k = p[k]
+	}
+	return s
+}

day75/problem_test.go

@@ -0,0 +1,30 @@
+package day75
+
+import (
+	"reflect"
+	"testing"
+)
+
+var testcases = []struct {
+	input, expected []int
+}{
+	{[]int{0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15},
+		[]int{0, 2, 6, 9, 11, 15}},
+}
+
+func TestLongestIncreasingSubsequence(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := LongestIncreasingSubsequence(tc.input); !reflect.DeepEqual(tc.expected, result) {
+			t.Errorf("Expected %v got %v", tc.expected, result)
+		}
+	}
+}
+
+func BenchmarkLongestIncreasingSubsequence(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			LongestIncreasingSubsequence(tc.input)
+		}
+	}
+}