Refine

Signed-off-by: begeekmyfriend <begeekmyfriend@gmail.com>

Author: begeekmyfriend

092_reverse_linked_list_ii/reverse_list.c

@@ -8,27 +8,25 @@ struct ListNode {
 
 static struct ListNode* reverseBetween(struct ListNode* head, int m, int n)
 {
-    int len = n - m + 1;
-    if (len == 1) {
-        return head;
-    }
-
+    int i;
     struct ListNode dummy;
-    struct ListNode *p = head;
     struct ListNode *prev = &dummy;
-    prev->next = p;
-    while (--m > 0) {
-        prev = p;
-        p = p->next;
+    prev->next = head;
+
+    for (i = 1; i < m; i++) {
+        prev = prev->next;
     }
 
-    struct ListNode *q = p->next;
-    while (--len > 0) {
+    struct ListNode *p = prev->next;
+    for (i = m; i < n; i++) {
+        struct ListNode *q = p->next;
+        /* deletion */
         p->next = q->next;
+        /* insertion */
         q->next = prev->next;
         prev->next = q;
-        q = p->next;
     }
+
     return dummy.next;
 }
 

206_reverse_linked_list/reverse_list.c

@@ -6,27 +6,39 @@ struct ListNode {
     struct ListNode *next;
 };
 
-static void recursive(struct ListNode *dummy, struct ListNode *prev, struct ListNode *p)
+static struct ListNode *recursive(struct ListNode *prev, struct ListNode *p)
 {
-    if (p != NULL) {
-        prev->next = p->next;
-        p->next = dummy->next;
-        dummy->next = p;
-        recursive(dummy, prev, prev->next);
+    if (p == NULL) {
+        return prev;
     }
+
+    struct ListNode *q = p->next;
+    p->next = prev;
+    return recursive(p, q);
 }
 
 static struct ListNode *reverseList(struct ListNode *head)
 {
-    if (head == NULL) {
-        return NULL;
+    return recursive(NULL, head);
+}
+
+
+/* Iteration */
+#if 0
+static struct ListNode *reverseList(struct ListNode *head)
+{
+    struct ListNode *prev = NULL;
+    struct ListNode *p = head;
+    while (p != NULL) {
+        struct ListNode *q = p->next;
+        p->next = prev;
+        prev = p;
+        p = q;
     }
 
-    struct ListNode dummy;
-    dummy.next = head;
-    recursive(&dummy, head, head->next);
-    return dummy.next;
+    return prev;
 }
+#endif
 
 int main(int argc, char **argv)
 {