From a4291d8a8c057e9649e2b0ee15aeab4ae9a3b032 Mon Sep 17 00:00:00 2001
From: Xieyang Liu <lxieyang@umich.edu>
Date: Sat, 13 Feb 2016 15:51:34 -0500
Subject: [PATCH 1/2] revised: merge k sorted lists

---
 C++/chapSorting.tex | 49 +++++++++++++++++++++++++--------------------
 1 file changed, 27 insertions(+), 22 deletions(-)

diff --git a/C++/chapSorting.tex b/C++/chapSorting.tex
index c20162d4..f686e0a3 100644
--- a/C++/chapSorting.tex
+++ b/C++/chapSorting.tex
@@ -101,31 +101,36 @@ \subsubsection{代码}
 // TODO: 会超时
 class Solution {
 public:
-    ListNode *mergeKLists(vector<ListNode *> &lists) {
-        if (lists.size() == 0) return nullptr;
 
-        ListNode *p = lists[0];
-        for (int i = 1; i < lists.size(); i++) {
-            p = mergeTwoLists(p, lists[i]);
+    ListNode * mergeTwo(ListNode * l1, ListNode * l2){
+        if(!l1) return l2;
+        if(!l2) return l1;
+        ListNode dummy(-1);
+        ListNode * p = &dummy;
+        for(; l1 && l2; p = p->next){
+            if(l1->val > l2->val){
+                p->next = l2; l2 = l2->next;
+            }
+            else{
+                p->next = l1; l1 = l1->next;
+            }
         }
-        return p;
+        p->next = l1 ? l1 : l2;
+        return dummy.next;
     }
 
-    // Merge Two Sorted Lists
-    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
-        ListNode head(-1);
-        for (ListNode* p = &head; l1 != nullptr || l2 != nullptr; p = p->next) {
-            int val1 = l1 == nullptr ? INT_MAX : l1->val;
-            int val2 = l2 == nullptr ? INT_MAX : l2->val;
-            if (val1 <= val2) {
-                p->next = l1;
-                l1 = l1->next;
-            } else {
-                p->next = l2;
-                l2 = l2->next;
-            }
+    ListNode* mergeKLists(vector<ListNode*>& lists) {
+        if(lists.size() == 0) return nullptr;
+
+        // multi pass
+        deque<ListNode *> dq(lists.begin(), lists.end());
+        while(dq.size() > 1){
+            ListNode * first = dq.front(); dq.pop_front();
+            ListNode * second = dq.front(); dq.pop_front();
+            dq.push_back(mergeTwo(first,second));
         }
-        return head.next;
+
+        return dq.front();
     }
 };
 \end{Code}
@@ -276,7 +281,7 @@ \subsubsection{代码}
 public:
     int firstMissingPositive(vector<int>& nums) {
         bucket_sort(nums);
-        
+
         for (int i = 0; i < nums.size(); ++i)
             if (nums[i] != (i + 1))
                 return i + 1;
@@ -385,7 +390,7 @@ \subsubsection{代码3}
 class Solution {
 public:
     void sortColors(vector<int>& nums) {
-        partition(partition(nums.begin(), nums.end(), bind1st(equal_to<int>(), 0)), 
+        partition(partition(nums.begin(), nums.end(), bind1st(equal_to<int>(), 0)),
                 nums.end(), bind1st(equal_to<int>(), 1));
     }
 };

From d4ee008ca19c3c58af54a92214f5d09a35dd9057 Mon Sep 17 00:00:00 2001
From: Xieyang Liu <lxieyang@umich.edu>
Date: Sat, 13 Feb 2016 15:52:48 -0500
Subject: [PATCH 2/2] revised merge k sorted lists

---
 C++/chapSorting.tex | 1 -
 1 file changed, 1 deletion(-)

diff --git a/C++/chapSorting.tex b/C++/chapSorting.tex
index f686e0a3..f92c115a 100644
--- a/C++/chapSorting.tex
+++ b/C++/chapSorting.tex
@@ -98,7 +98,6 @@ \subsubsection{代码}
 \begin{Code}
 //LeetCode, Merge k Sorted Lists
 // 时间复杂度O(n1+n2+...)，空间复杂度O(1)
-// TODO: 会超时
 class Solution {
 public: