Merge pull request #5 from colorbox/21

21. Merge Two Sorted Lists

Author: colorbox

21/1.cpp

@@ -0,0 +1,50 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode() : val(0), next(nullptr) {}
+ *     ListNode(int x) : val(x), next(nullptr) {}
+ *     ListNode(int x, ListNode *next) : val(x), next(next) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
+        if(list1 == nullptr)return list2;
+        if(list2 == nullptr)return list1;
+
+        ListNode *ret;
+        if(list1->val < list2->val){
+            ret = list1;
+            list1 = list1->next;
+        } else{
+            ret = list2;
+            list2 = list2->next;
+        }
+        ListNode *current = ret;
+
+        while(list1 != nullptr || list2 != nullptr){
+            if(list1 == nullptr){
+                current->next = list2;
+                return ret;
+            }
+
+            if(list2 == nullptr){
+                current->next = list1;
+                return ret;
+            }
+
+            if(list1->val < list2->val){
+                current->next = list1;
+                list1 = list1->next;
+            }else{
+                current->next = list2;
+                list2 = list2->next;
+            }
+            current = current->next;
+        }
+
+        return ret;
+    }
+};

21/2.cpp

@@ -0,0 +1,51 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode() : val(0), next(nullptr) {}
+ *     ListNode(int x) : val(x), next(nullptr) {}
+ *     ListNode(int x, ListNode *next) : val(x), next(next) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
+        if(list1 == nullptr)return list2;
+        if(list2 == nullptr)return list1;
+
+        // always list1 <= list2
+        if(list1->val > list2->val){
+            swap(list1, list2);
+        }
+
+        ListNode* ret = list1;
+        list1 = list1->next;
+
+        ListNode *current = ret;
+
+        while(list1 != nullptr && list2 != nullptr){
+            // always list1 <= list2
+            if(list1->val > list2->val){
+                swap(list1, list2);
+            }
+
+            current->next = list1;
+            list1 = list1->next;
+
+            current = current->next;
+        }
+
+        if(list1 == nullptr){
+            current->next = list2;
+            return ret;
+        }
+
+        if(list2 == nullptr){
+            current->next = list1;
+            return ret;
+        }
+
+        return ret;
+    }
+};

21/3.cpp

@@ -0,0 +1,36 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode() : val(0), next(nullptr) {}
+ *     ListNode(int x) : val(x), next(nullptr) {}
+ *     ListNode(int x, ListNode *next) : val(x), next(next) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
+        ListNode ret = ListNode();
+        ListNode *current = &ret;
+
+        while(list1 != nullptr && list2 != nullptr){
+            if(list1->val > list2->val){
+                swap(list1, list2);
+            }
+
+            current->next = list1;
+            current = current->next;
+            list1 = list1->next;
+        }
+
+        if(list1 == nullptr){
+            current->next = list2;
+        }
+        if(list2 == nullptr){
+            current->next = list1;
+        }
+
+        return ret.next;
+    }
+};

21/4.cpp

@@ -0,0 +1,39 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode() : val(0), next(nullptr) {}
+ *     ListNode(int x) : val(x), next(nullptr) {}
+ *     ListNode(int x, ListNode *next) : val(x), next(next) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
+        ListNode root = ListNode();
+        ListNode *current = &root;
+
+        ListNode *smaller = list1;
+        ListNode *bigger = list2;
+
+        while (smaller && bigger) {
+            if (smaller->val > bigger->val) {
+                swap(smaller, bigger);
+            }
+
+            current->next = smaller;
+            current = current->next;
+            smaller = smaller->next;
+        }
+
+        if (smaller) {
+            current->next = smaller;
+        }
+        if (bigger) {
+            current->next = bigger;
+        }
+
+        return root.next;
+    }
+};