Merge two sorted lists

Signed-off-by: begeekmyfriend <[email protected]>

021_merge_two_sorted_lists/Makefile

@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test merge_lists.c

021_merge_two_sorted_lists/merge_lists.c

@@ -0,0 +1,56 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+struct ListNode {
+    int val;
+    struct ListNode *next;
+};
+
+static struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2)
+{
+    struct ListNode dummy, *tail = &dummy;
+    dummy.next = NULL;
+
+    while (l1 != NULL || l2 != NULL) {
+        struct ListNode *node = malloc(sizeof(*node));
+        node->next = NULL;
+        tail->next = node;
+        tail = node;
+        if (l1 != NULL) {
+            if (l2 != NULL) {
+                if (l1->val < l2->val) {
+                    node->val = l1->val;
+                    l1 = l1->next;
+                } else {
+                    node->val = l2->val;
+                    l2 = l2->next;
+                }
+            } else {
+                node->val = l1->val;
+                l1 = l1->next;
+            }
+        } else {
+            node->val = l2->val;
+            l2 = l2->next;
+        }
+    }
+
+    return dummy.next;
+}
+
+int main(int argc, char **argv)
+{
+    struct ListNode l1;
+    l1.val = 2;
+    l1.next = NULL;
+    struct ListNode l2;
+    l2.val = 1;
+    l2.next = NULL;
+    struct ListNode * list = mergeTwoLists(&l1, &l2);
+    while (list != NULL) {
+        printf("%d ", list->val);
+        list = list->next;
+    }
+    printf("\n");
+    return 0;
+}