delete middle

deletemiddle/deletemiddle.go

@@ -0,0 +1,42 @@
+package deletemiddle
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+func length(node *ListNode) int {
+	length := 0
+	for node != nil {
+		length++
+		node = node.Next
+	}
+
+	return length
+}
+
+func nth(node *ListNode, n int) *ListNode {
+	for i := 0; i < n; i++ {
+		node = node.Next
+	}
+
+	return node
+}
+
+func deleteMiddle(head *ListNode) *ListNode {
+	length := length(head)
+	if length <= 1 {
+		return nil
+	}
+
+	midIndex := length / 2
+	preceeding := nth(head, midIndex-1)
+	preceeding.Next = preceeding.Next.Next
+
+	return head
+}
+
+func Delete(head *ListNode) *ListNode {
+	return deleteMiddle(head)
+
+}

deletemiddle/deletemiddle_test.go

@@ -0,0 +1,46 @@
+package deletemiddle_test
+
+import (
+	"testing"
+
+	dm "git.jxs.me/leetgo/deletemiddle"
+	"github.com/stretchr/testify/require"
+)
+
+func buildList(values []int) *dm.ListNode {
+	var result *dm.ListNode
+
+	for i := len(values) - 1; i >= 0; i-- {
+		result = &dm.ListNode{Val: values[i], Next: result}
+	}
+
+	return result
+}
+
+func TestEmpty(t *testing.T) {
+	var head *dm.ListNode
+	require.Nil(t, dm.Delete(head))
+}
+
+func TestOne(t *testing.T) {
+	head := buildList([]int{1})
+	require.Nil(t, dm.Delete(head))
+}
+
+func TestTwo(t *testing.T) {
+	head := buildList([]int{2, 1})
+	expected := buildList([]int{2})
+	require.Equal(t, expected, dm.Delete(head))
+}
+
+func TestFour(t *testing.T) {
+	head := buildList([]int{1, 2, 3, 4})
+	expected := buildList([]int{1, 2, 4})
+	require.Equal(t, expected, dm.Delete(head))
+}
+
+func TestExample1(t *testing.T) {
+	head := buildList([]int{1, 3, 4, 7, 1, 2, 6})
+	expected := buildList([]int{1, 3, 4, 1, 2, 6})
+	require.Equal(t, expected, dm.Delete(head))
+}