Add solution and test-cases and README for problem 21

Author: 0xff-dev

leetcode/1-100/0021.Merge-Two-Sorted-Lists/README.md

@@ -0,0 +1,36 @@
+# [21.Merge Two Sorted Lists][title]
+
+## Description
+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:** 
+![exampl1](./merge_ex1.jpg)
+
+```
+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]
+```
+
+## 结语
+
+如果你同我一样热爱数据结构、算法、LeetCode，可以关注我 GitHub 上的 LeetCode 题解：[awesome-golang-algorithm][me]
+
+[title]: https://leetcode.com/problems/merge-two-sorted-lists/
+[me]: https://github.com/kylesliu/awesome-golang-algorithm

leetcode/1-100/0021.Merge-Two-Sorted-Lists/Solution.go

@@ -27,3 +27,21 @@ func mergeTwoLists(l1 *ListNode, l2 *ListNode) *ListNode {
 
 return head.Next
 }
+
+func mergeTwoLists1(l1, l2 *ListNode) *ListNode {
+if l1 == nil {
+return l2
+}
+if l2 == nil {
+return l1
+}
+n := &ListNode{}
+if l1.Val < l2.Val {
+n.Val = l1.Val
+n.Next = mergeTwoLists1(l1.Next, l2)
+} else {
+n.Val = l2.Val
+n.Next = mergeTwoLists1(l1, l2.Next)
+}
+return n
+}

leetcode/1-100/0021.Merge-Two-Sorted-Lists/Solution_test.go

@@ -10,7 +10,8 @@ func TestSolution(t *testing.T) {
 data1 := []int{1, 2, 4}
 data2 := []int{1, 3, 4}
 
-got := mergeTwoLists(MakeListNote(data1), MakeListNote(data2))
+l1, l2 := MakeListNote(data1), MakeListNote(data2)
+got := mergeTwoLists(l1, l2)
 want := MakeListNote([]int{1, 1, 2, 3, 4, 4})
 
 if !Equal(got, want) {
@@ -20,13 +21,23 @@ func TestSolution(t *testing.T) {
 PrintList(want)
 t.Error("GOT:", got, "WANT:", want)
 }
+
+got = mergeTwoLists1(l1, l2)
+if !Equal(got, want) {
+fmt.Print("GOT:")
+PrintList(got)
+fmt.Print("WANT:")
+PrintList(want)
+t.Error("GOT:", got, "WANT:", want)
+}
 })
 
 t.Run("Test-2", func(t *testing.T) {
 data1 := []int{1, 2, 4, 5, 6, 7}
 data2 := []int{1, 3, 4, 9, 10}
 
-got := mergeTwoLists(MakeListNote(data1), MakeListNote(data2))
+l1, l2 := MakeListNote(data1), MakeListNote(data2)
+got := mergeTwoLists(l1, l2)
 want := MakeListNote([]int{1, 1, 2, 3, 4, 4, 5, 6, 7, 9, 10})
 
 if !Equal(got, want) {
@@ -36,6 +47,15 @@ func TestSolution(t *testing.T) {
 PrintList(want)
 t.Error("GOT:", got, "WANT:", want)
 }
+
+got = mergeTwoLists1(l1, l2)
+if !Equal(got, want) {
+fmt.Print("GOT:")
+PrintList(got)
+fmt.Print("WANT:")
+PrintList(want)
+t.Error("GOT:", got, "WANT:", want)
+}
 })
 }