simplified

Author: Victor

23. Merge k Sorted Lists.c

@@ -7,64 +7,61 @@ Merge k sorted linked lists and return it as one sorted list. Analyze and descri
 /**
  * Definition for singly-linked list.
  * struct ListNode {
- *     int val;
- *     struct ListNode *next;
+ *     int val;
+ *     struct ListNode *next;
  * };
  */
 struct ListNode *merge(struct ListNode *a, struct ListNode *b) {
-    struct ListNode *head, *prev, *c;
-    head = prev = NULL;
-    while (a && b) {
-        if (a->val < b->val) {
-            c = a;
-            a = a->next;
-        } else {
-            c = b;
-            b = b->next;
-        }
-        if (!head) head = c;
-        if (prev) prev->next = c;
-        prev = c;
-    }
-    if (!head) head = a ? a : b;
-    if (prev) prev->next = a ? a : b;
-    return head;
+    struct ListNode head, *prev, *c;
+    prev = &head;
+    while (a && b) {
+        if (a->val < b->val) {
+            c = a;
+            a = a->next;
+        } else {
+            c = b;
+            b = b->next;
+        }
+        prev->next = c;
+        prev = c;
+    }
+    prev->next = a ? a : b;
+    return head.next;
 }
 struct ListNode *divide_and_merge(struct ListNode **lists, int start, int end) {
-    int mid;
-    struct ListNode *a, *b;
-    
-    if (start == end) return lists[start];
-    
-    mid = start + (end - start) / 2;
-    
-    a = divide_and_merge(lists, start, mid);
-    b = divide_and_merge(lists, mid + 1, end);
-    
-    return merge(a, b);
+    int mid;
+    struct ListNode *a, *b;
+    
+    if (start == end) return lists[start];
+    
+    mid = start + (end - start) / 2;
+    
+    a = divide_and_merge(lists, start, mid);
+    b = divide_and_merge(lists, mid + 1, end);
+    
+    return merge(a, b);
 }
 struct ListNode* mergeKLists(struct ListNode** lists, int listsSize) {
-    struct ListNode *head = NULL;
-​
-    if (listsSize == 0) return NULL;
-​
-#if 0  // 245ms
-    int i;
-    struct ListNode *a, *b;
-    
-    a = lists[0];
-    for (i = 1; i < listsSize; i ++) {
-        b = lists[i];
-        a = merge(a, b);
-    }
-    head = a;
-#else  // 9ms   O(NKlogK) N is average length of a list, K is number of lists
-    head = divide_and_merge(lists, 0, listsSize - 1);
+    struct ListNode *head = NULL;
+
+    if (listsSize == 0) return NULL;
+
+#if 0  // 245ms
+    int i;
+    struct ListNode *a, *b;
+    
+    a = lists[0];
+    for (i = 1; i < listsSize; i ++) {
+        b = lists[i];
+        a = merge(a, b);
+    }
+    head = a;
+#else  // 9ms   O(NKlogK) N is average length of a list, K is number of lists
+    head = divide_and_merge(lists, 0, listsSize - 1);
 #endif
-    return head;
+    return head;
 }
 
-
 /*
 Difficulty:Hard
 Total Accepted:159.5K