vault backup: 2022-09-08 15:40:52

.obsidian/app.json

@@ -13,5 +13,7 @@
   "defaultViewMode": "preview",
   "fileSortOrder": "byCreatedTime",
   "showFrontmatter": true,
-  "autoPairMarkdown": false
+  "autoPairMarkdown": false,
+  "strictLineBreaks": true,
+  "readableLineLength": true
 }

OJ notes/pages/Leetcode Add-Two-Numbers.md

@@ -74,6 +74,62 @@ You may assume the two numbers do not contain any leading zero, except the numbe
 
 Done by using elementary math.
 
-Use only one 
+Use only one variable `tmp` to keep track of sum of 2
+digits and carries.
 
 ### Solution
+
+```cpp
+/**
+ * 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 {
+  ListNode *appendNumber(ListNode *ptr, int num) {
+    ListNode *ans = new ListNode(num, nullptr);
+    ptr->next = ans;
+
+    return ans;
+  }
+
+public:
+  ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
+    ListNode *ptr1 = l1, *ptr2 = l2;
+
+    // the minimum size is 1, so we can safely do this.
+    int tmp = ptr1->val + ptr2->val;
+
+    ListNode *ans = new ListNode(tmp % 10);
+
+    ListNode *tail = ans;
+
+    tmp /= 10;
+    ptr1 = ptr1->next;
+    ptr2 = ptr2->next;
+
+    while (ptr1 || ptr2 || tmp) {
+      if (ptr1) {
+        tmp += ptr1->val;
+        ptr1 = ptr1->next;
+      }
+
+      if (ptr2) {
+        tmp += ptr2->val;
+        ptr2 = ptr2->next;
+      }
+
+      tail = appendNumber(tail, tmp % 10);
+
+      tmp /= 10;
+    }
+
+    return ans;
+  }
+};
+```