Refine

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

Author: begeekmyfriend

138_copy_list_with_random_pointer/copy_list.c

@@ -1,36 +1,39 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-struct RandomListNode {
-    int label;
-    struct RandomListNode *next;
-    struct RandomListNode *random;
+struct Node {
+    int val;
+    struct Node *next;
+    struct Node *random;
 };
 
-static struct RandomListNode *copyRandomList(struct RandomListNode *head)
+static struct Node *copyRandomList(struct Node *head)
 {
     if (head == NULL) {
         return NULL;
     }
 
-    struct RandomListNode *p, *new;
+    /* copy and redirect next pointer */
+    struct Node *p, *new;
     for (p = head; p != NULL; p = p->next->next) {
         new = malloc(sizeof(*new));
-        new->label = p->label;
+        new->val = p->val;
         new->next = p->next;
         p->next = new;
     }
 
+    /* clone random pointer */
     for (p = head; p != NULL; p = p->next->next) {
         new = p->next;
         new->random = p->random != NULL ? p->random->next : NULL;
     }
 
-    struct RandomListNode dummy;
-    struct RandomListNode *prev = &dummy;
+    struct Node dummy;
+    struct Node *prev = &dummy;
     for (p = head; p != NULL; p = p->next) {
         new = p->next;
         p->next = new->next;
+        /* correct the actual next pointer of the new list */
         prev->next = new;
         prev = new;
         new->next = NULL;
@@ -42,10 +45,10 @@ static struct RandomListNode *copyRandomList(struct RandomListNode *head)
 int main(int argc, char **argv)
 {
     int i, count = argc - 1;
-    struct RandomListNode *head = NULL, *p, *prev;
+    struct Node *head = NULL, *p, *prev;
     for (i = 0; i < count; i++) {
         p = malloc(sizeof(*p));
-        p->label = atoi(argv[i + 1]);
+        p->val = atoi(argv[i + 1]);
         p->next = NULL;
         p->random = NULL;
         if (head == NULL) {
@@ -57,26 +60,26 @@ int main(int argc, char **argv)
         prev = p;
     }
 
-    struct RandomListNode *r = head;
-    struct RandomListNode *q = p = copyRandomList(head);
+    struct Node *r = head;
+    struct Node *q = p = copyRandomList(head);
 
     for (r = head; r != NULL; r = r->next) {
-        printf("%d ", r->label);
+        printf("%d ", r->val);
     }
     printf("\n");
 
     for (r = head; r != NULL; r = r->random) {
-        printf("%d ", r->label);
+        printf("%d ", r->val);
     }
     printf("\n");
 
     for (; p != NULL; p = p->next) {
-        printf("%d ", p->label);
+        printf("%d ", p->val);
     }
     printf("\n");
 
     for (; q != NULL; q = q->random) {
-        printf("%d ", q->label);
+        printf("%d ", q->val);
     }
     printf("\n");
     return 0;

143_reorder_list/reorder_list.c

@@ -6,47 +6,48 @@ struct ListNode {
     struct ListNode *next;
 };
 
-static void reverse(struct ListNode *dummy)
-{
-    struct ListNode *prev = dummy->next;
-    if (prev != NULL) {
-        struct ListNode *p = prev->next;
-        while (p != NULL) {
-            prev->next = p->next;
-            p->next = dummy->next;
-            dummy->next = p;
-            p = prev->next;
-        }
-    }
-}
-
 static void reorderList(struct ListNode *head)
 {
-    if (head == NULL) {
+    if (head == NULL || head->next == NULL) {
         return;
     }
 
     int count = 0;
-    struct ListNode *p = head;
-    struct ListNode *q = p;
+    struct ListNode dummy;
+    struct ListNode *prev = &dummy;
+    struct ListNode *p, *q;
 
     /* locate half length */
-    for (; p != NULL; p = p->next) {
+    dummy.next = head;
+    for (p = head, q = head; q != NULL; q = q->next) {
         if ((++count & 0x1) == 0) {
-            q = q->next;
+            prev = p;
+            p = p->next;
         }
     }
 
     /* reverse latter half list */
-    reverse(q);
+    while (p->next != NULL) {
+        q = p->next;
+        /* deletion */
+        p->next = q->next;
+        /* insertion */
+        q->next = prev->next;
+        prev->next = q;
+    }
 
-    /* insert each element */
-    struct ListNode *r;
-    for (p = head, r = q->next; r != NULL; p = r->next, r = q->next) {
-        q->next = r->next;
-        r->next = p->next;
-        p->next = r;
-    } 
+    /* insert each element interleavingly */
+    struct ListNode *last = prev;
+    p = head;
+    while (p != last) {
+        q = last->next;
+        /* deletion */
+        last->next = q->next;
+        /* insertion */
+        q->next = p->next;
+        p->next = q;
+        p = q->next;
+    }
 }
 
 int main(int argc, char **argv)