Solve merge-two-sorted-lists

0021-merge-two-sorted-lists/README.txt

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+https://leetcode.com/problems/merge-two-sorted-lists/
+
+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.

0021-merge-two-sorted-lists/main1.c

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+#include <stdlib.h>
+#include <stdio.h>
+#include <assert.h>
+#include <string.h>
+#include <limits.h>
+#include <stdbool.h>
+
+struct ListNode {
+	int val;
+	struct ListNode *next;
+};
+
+struct ListNode *
+mergeTwoLists(struct ListNode *list1, struct ListNode *list2)
+{
+	if (list1 == NULL)
+		return list2;
+	if (list2 == NULL)
+		return list1;
+	struct ListNode *first;
+	struct ListNode *res;
+	if (list1->val <= list2->val) {
+		res = list1;
+		list1 = list1->next;
+	} else {
+		res = list2;
+		list2 = list2->next;
+	}
+	first = res;
+	while (list1 != NULL && list2 != NULL) {
+		if (list1->val <= list2->val) {
+			res->next = list1;
+			res = list1;
+			list1 = list1->next;
+		} else {
+			res->next = list2;
+			res = list2;
+			list2 = list2->next;
+		}
+	}
+	if (list1 != NULL)
+		res->next = list1;
+	else
+		res->next = list2;
+	return first;
+}
+
+static struct ListNode *
+make_list(const int *values, int count)
+{
+	if (count == 0)
+		return NULL;
+	struct ListNode *nodes = malloc(sizeof(nodes[0]) * count);
+	for (int i = 0; i < count; ++i) {
+		nodes[i].val = values[i];
+		if (i != 0)
+			nodes[i - 1].next = &nodes[i];
+	}
+	nodes[count - 1].next = NULL;
+	return nodes;
+}
+
+static bool
+lists_are_eq(const struct ListNode *left, const struct ListNode *right)
+{
+	while (left != NULL && right != NULL) {
+		if (left->val != right->val)
+			return false;
+		left = left->next;
+		right = right->next;
+	}
+	return left == NULL && right == NULL;
+}
+
+static inline void
+check(bool ok)
+{
+	if (!ok)
+		abort();
+}
+
+int
+main()
+{
+	{
+		struct ListNode *list1 = make_list(
+			(const int[]){1, 2, 4}, 3);
+		struct ListNode *list2 = make_list(
+			(const int[]){1, 3, 4}, 3);
+		struct ListNode *expected = make_list(
+			(const int[]){1, 1, 2, 3, 4, 4}, 6);
+		struct ListNode *actual = mergeTwoLists(list1, list2);
+		check(lists_are_eq(actual, expected));
+		free(expected);
+		free(list1);
+		free(list2);
+	}
+	{
+		struct ListNode *list1 = make_list((const int[]){}, 0);
+		struct ListNode *list2 = make_list((const int[]){}, 0);
+		struct ListNode *expected = make_list((const int[]){}, 0);
+		struct ListNode *actual = mergeTwoLists(list1, list2);
+		check(lists_are_eq(actual, expected));
+		free(expected);
+		free(list1);
+		free(list2);
+	}
+	{
+		struct ListNode *list1 = make_list((const int[]){}, 0);
+		struct ListNode *list2 = make_list((const int[]){0}, 1);
+		struct ListNode *expected = make_list((const int[]){0}, 1);
+		struct ListNode *actual = mergeTwoLists(list1, list2);
+		check(lists_are_eq(actual, expected));
+		free(expected);
+		free(list1);
+		free(list2);
+	}
+	{
+		struct ListNode *list1 = make_list(
+			(const int[]){3, 5}, 2);
+		struct ListNode *list2 = make_list(
+			(const int[]){1, 4, 6, 7}, 4);
+		struct ListNode *expected = make_list(
+			(const int[]){1, 3, 4, 5, 6, 7}, 6);
+		struct ListNode *actual = mergeTwoLists(list1, list2);
+		check(lists_are_eq(actual, expected));
+		free(expected);
+		free(list1);
+		free(list2);
+	}
+	{
+		struct ListNode *list1 = make_list(
+			(const int[]){3, 6, 7, 10}, 4);
+		struct ListNode *list2 = make_list(
+			(const int[]){-1, 2, 15}, 3);
+		struct ListNode *expected = make_list(
+			(const int[]){-1, 2, 3, 6, 7, 10, 15}, 7);
+		struct ListNode *actual = mergeTwoLists(list1, list2);
+		check(lists_are_eq(actual, expected));
+		free(expected);
+		free(list1);
+		free(list2);
+	}
+	return 0;
+}