add new solutions

solutions/0/q21/solution.go

@@ -0,0 +1,36 @@
+package q21
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+func mergeTwoLists(list1 *ListNode, list2 *ListNode) *ListNode {
+	root := &ListNode{}
+	cur := root
+
+	for {
+		if list1 == nil && list2 == nil {
+			return root.Next
+		}
+		if list1 == nil {
+			cur.Next = list2
+			return root.Next
+		} else if list2 == nil {
+			cur.Next = list1
+			return root.Next
+		} else if list1.Val < list2.Val {
+			cur.Next = list1
+			cur = cur.Next
+			list1 = list1.Next
+			cur.Next = nil
+		} else {
+			cur.Next = list2
+			cur = cur.Next
+			list2 = list2.Next
+			cur.Next = nil
+		}
+	}
+}
+
+var _ = mergeTwoLists