Add editor config, add two lists sum solution

Author: chachaxw

.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+charset = utf-8
+indent_style = space
+indent_size = 4
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true

a.out renamed to leetcode/linked_list/two_lists_sum

@@ -0,0 +1,87 @@
+/**
+ * @Author: Chacha 
+ * @Date: 2019-02-14 10:00:00 
+ * @Last Modified by: Chacha
+ * @Last Modified time: 2019-02-14 10:17:20
+ */
+
+#include<iostream>
+#include<string>
+using namespace std;
+
+/** 
+ * Definition for singly-linked list(单向链表)
+ * Source: https://zh.wikipedia.org/wiki/链表
+ */
+struct ListNode {
+    int val;
+    ListNode *next;
+    ListNode(int x) : val(x), next(NULL) {}
+};
+
+class Solution {
+public:
+    /**
+     * You have two numbers represented by a linked list, where each node contains a single digit.
+     * The digits are stored in reverse order, such that the 1’s digit is at the head of the list.
+     * Write a function that adds the two numbers and returns the sum as a linked list.
+     *
+     * Example:
+     *  Given two lists, 3->1->5->null and 5->9->2->null, return 8->0->8->null
+     */
+    ListNode* twoListsSum(ListNode* l1, ListNode* l2) {
+        if (l1 == NULL && l2 == NULL) {
+            return NULL;
+        }
+
+        ListNode* sumList = new ListNode(0);
+        ListNode* tempList = sumList;
+
+        int carry = 0;
+        while((l1 != NULL) || (l2 != NULL) || (carry != 0)){
+            int l1_val = (l1 == NULL) ? 0 : l1->val;
+            int l2_val = (l2 == NULL) ? 0 : l2->val;
+
+            tempList->val = (carry + l1_val + l2_val) % 10;
+            carry = (carry + l1_val + l2_val) / 10;
+
+            if (l1 != NULL) l1 = l1->next;
+            if (l2 != NULL) l2 = l2->next;
+
+            // return sumlist before generating new ListNode
+            if ((l1 == NULL) && (l2 == NULL) && (carry == 0)) {
+                return sumList;
+            }
+            
+            tempList->next = new ListNode(0);
+            tempList = tempList->next;
+        }
+        
+        return sumList;
+    }
+};
+
+/* Function to print nodes in a given linked list */
+void printList(ListNode *node) { 
+    while (node != NULL) { 
+        printf("%d ", node->val);
+        node = node->next; 
+    }
+}
+
+int main()
+{
+    ListNode* l1 = new ListNode(3);
+    l1->next = new ListNode(1);
+    l1->next->next = new ListNode(5);
+
+    ListNode* l2 = new ListNode(5);
+    l2->next = new ListNode(9);
+    l2->next->next = new ListNode(2);
+
+    ListNode* sum = Solution().twoListsSum(l1, l2);
+
+    printList(sum);
+
+    return 0;
+}