From 7b82c2490731ce4ed1f073db3ab1868d67b9ce87 Mon Sep 17 00:00:00 2001
From: Jason Staten <code@jxs.me>
Date: Tue, 4 Oct 2022 22:11:43 -0600
Subject: [PATCH] mergesorted

---
 mergesorted/mergesorted.go      | 42 ++++++++++++++++++++++
 mergesorted/mergesorted_test.go | 63 +++++++++++++++++++++++++++++++++
 mergesorted/readme.md           | 33 +++++++++++++++++
 3 files changed, 138 insertions(+)
 create mode 100644 mergesorted/mergesorted.go
 create mode 100644 mergesorted/mergesorted_test.go
 create mode 100644 mergesorted/readme.md

diff --git a/mergesorted/mergesorted.go b/mergesorted/mergesorted.go
new file mode 100644
index 0000000..d3132ed
--- /dev/null
+++ b/mergesorted/mergesorted.go
@@ -0,0 +1,42 @@
+package mergesorted
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+func reverse(list *ListNode) *ListNode {
+	var result *ListNode
+	for list != nil {
+		result = &ListNode{Val: list.Val, Next: result}
+		list = list.Next
+	}
+
+	return result
+}
+
+func mergeTwoLists(list1 *ListNode, list2 *ListNode) *ListNode {
+
+	var result *ListNode
+	for list1 != nil || list2 != nil {
+		if list1 == nil {
+			result = &ListNode{Val: list2.Val, Next: result}
+			list2 = list2.Next
+		} else if list2 == nil {
+			result = &ListNode{Val: list1.Val, Next: result}
+			list1 = list1.Next
+		} else if list1.Val < list2.Val {
+			result = &ListNode{Val: list1.Val, Next: result}
+			list1 = list1.Next
+		} else {
+			result = &ListNode{Val: list2.Val, Next: result}
+			list2 = list2.Next
+		}
+	}
+
+	return reverse(result)
+}
+
+func MergeTwoLists(list1 *ListNode, list2 *ListNode) *ListNode {
+	return mergeTwoLists(list1, list2)
+}
diff --git a/mergesorted/mergesorted_test.go b/mergesorted/mergesorted_test.go
new file mode 100644
index 0000000..d75823b
--- /dev/null
+++ b/mergesorted/mergesorted_test.go
@@ -0,0 +1,63 @@
+package mergesorted_test
+
+import (
+	"testing"
+
+	ms "git.jxs.me/leetgo/mergesorted"
+	"github.com/stretchr/testify/require"
+)
+
+func buildList(values []int) *ms.ListNode {
+	var result *ms.ListNode
+
+	for i := len(values) - 1; i >= 0; i-- {
+		result = &ms.ListNode{Val: values[i], Next: result}
+	}
+
+	return result
+}
+
+func TestEmpty(t *testing.T) {
+	require.Nil(t, nil, ms.MergeTwoLists(nil, nil))
+}
+
+func TestEmptyRight(t *testing.T) {
+	left := buildList([]int{4, 5})
+	right := buildList([]int{})
+	res := ms.MergeTwoLists(left, right)
+	require.Equal(t, left, res)
+}
+
+func TestEmptyLeft(t *testing.T) {
+	left := buildList([]int{})
+	right := buildList([]int{1, 2})
+	res := ms.MergeTwoLists(left, right)
+	require.Equal(t, right, res)
+}
+
+func TestMix(t *testing.T) {
+	left := buildList([]int{1, 3})
+	right := buildList([]int{2, 4})
+	res := ms.MergeTwoLists(left, right)
+
+	expected := buildList([]int{1, 2, 3, 4})
+	require.Equal(t, expected, res)
+}
+
+func TestExample1(t *testing.T) {
+	left := buildList([]int{1, 3, 4})
+	right := buildList([]int{1, 2, 4})
+	res := ms.MergeTwoLists(left, right)
+
+	expected := buildList([]int{1, 1, 2, 3, 4, 4})
+	require.Equal(t, expected, res)
+}
+
+func TestExample2(t *testing.T) {
+	left := buildList([]int{})
+	right := buildList([]int{0})
+	res := ms.MergeTwoLists(left, right)
+
+	expected := buildList([]int{0})
+	require.Equal(t, expected, res)
+}
diff --git a/mergesorted/readme.md b/mergesorted/readme.md
new file mode 100644
index 0000000..437c0ec
--- /dev/null
+++ b/mergesorted/readme.md
@@ -0,0 +1,33 @@
+21. Merge Two Sorted Lists
+Easy
+
+You are given the heads of two sorted linked lists list1 and list2.
+
+Merge the two lists in a one sorted list. The list should be made by splicing together the nodes of the first two lists.
+
+Return the head of the merged linked list.
+
+ 
+
+Example 1:
+
+Input: list1 = [1,2,4], list2 = [1,3,4]
+Output: [1,1,2,3,4,4]
+
+Example 2:
+
+Input: list1 = [], list2 = []
+Output: []
+
+Example 3:
+
+Input: list1 = [], list2 = [0]
+Output: [0]
+
+ 
+
+Constraints:
+
+    The number of nodes in both lists is in the range [0, 50].
+    -100 <= Node.val <= 100
+    Both list1 and list2 are sorted in non-decreasing order.