Simple linked list structure

include/list.h

@@ -0,0 +1,56 @@
+#pragma once
+
+#include <stdio.h>
+#include <stdlib.h>
+
+/** Linked list data structure
+ */
+
+struct ListNode {
+    int val;
+    struct ListNode *next;
+};
+
+struct ListNode *list_create(int val) {
+    struct ListNode *node = malloc(sizeof(struct ListNode));
+    node->next = NULL;
+    node->val = val;
+    return node;
+}
+
+struct ListNode *list_insert(struct ListNode *list, int val) {
+    if (list == NULL) {
+        list = list_create(val);
+        return list;
+    } else {
+        struct ListNode *tail = list_create(val);
+        struct ListNode *current = list;
+        while (current->next != NULL) {
+            current = current->next;
+        }
+        current->next = tail;
+        return list;
+    }
+}
+
+void list_clear(struct ListNode *list) {
+    struct ListNode *current = list;
+    if (current == NULL) {
+        return;
+    }
+    while (current->next != NULL) {
+        struct ListNode *next = current->next;
+        free(current);
+        current = next;
+    }
+}
+
+void list_print(struct ListNode *list) {
+    struct ListNode *current = list;
+    printf("list: ");
+    while (current != NULL) {
+        printf("%d->", current->val);
+        current = current->next;
+    }
+    printf("\n");
+}

src/19.remove-nth-node-from-end-of-list.c

@@ -0,0 +1,82 @@
+#include "../include/list.h"
+
+
+/** Remove n-th element from linked list */
+struct ListNode *removeNthElement(struct ListNode *head, int n) {
+    int i=0;
+    if (n < 0) {
+        return head;
+    }
+    if (n == 0) {
+        return head->next;
+    }
+    struct ListNode *current = head;
+    while (i < n - 1 && current != NULL) {
+        current = current->next;
+        i++;
+    }
+    if (current != NULL && current->next != NULL && current->next->next != NULL) {
+        struct ListNode *to_remove = current->next;
+        current->next = current->next->next;
+        free(to_remove);
+    } else if (current != NULL && current->next != NULL) {
+        free(current->next);
+        current->next = NULL;
+    }
+    return head;
+}
+
+/** Length of a linked list */
+unsigned int list_length(struct ListNode *head) {
+    unsigned int length = 0;
+    struct ListNode *current = head;
+    while (current != NULL) {
+        current = current->next;
+        length++;
+    }
+    return length;
+}
+
+struct ListNode *removeNthFromEnd(struct ListNode *head, int n) {
+    if (n < 0) {
+        return head;
+    }
+    unsigned int length = list_length(head);
+    return removeNthElement(head, length - n);
+}
+
+
+void test_1() {
+    struct ListNode *l = NULL;
+    l = list_insert(l, 1);
+    l = list_insert(l, 2);
+    l = list_insert(l, 3);
+    l = list_insert(l, 4);
+    l = list_insert(l, 5);
+    struct ListNode *result_list = removeNthFromEnd(l, 2);
+    list_print(result_list);
+    list_clear(result_list);
+}
+
+void test_2() {
+    struct ListNode *l = NULL;
+    l = list_insert(l, 1);
+    struct ListNode *result_list = removeNthFromEnd(l, 1);
+    list_print(result_list);
+    list_clear(result_list);
+}
+
+void test_3() {
+    struct ListNode *l = NULL;
+    l = list_insert(l, 1);
+    l = list_insert(l, 2);
+    struct ListNode *result_list = removeNthFromEnd(l, 1);
+    list_print(result_list);
+    list_clear(result_list);
+}
+
+int main() {
+    test_1();
+    test_2();
+    test_3();
+}