###### tags: `leetcode`, `javascript`
# 【LeetCode】Javascript - #2 Add Two Numbers

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### 題目：

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

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### 大概翻譯：

給您兩個非空鏈表，表示兩個非負整數。 數位按相反順序存儲，每個節點包含一個數位。 將這兩個數位相加，並將總和作為鏈表返回。

您可以假設這兩個數位不包含任何前導零，除了數位0本身。

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例如：

Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]
Explanation: 342 + 465 = 807.

Input: l1 = [0], l2 = [0]
Output: [0]

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
Output: [8,9,9,9,0,0,0,1]

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var addTwoNumbers = function(l1, l2) {
    // 先創建一個節點，因為需要用它來做指向
    let headNode = new ListNode();
	
    // 跟踪當前節點，以便我們可以輕鬆地在末尾添加新節點
    let currNode = headNode;
	
    // 根據上一次迴圈結果，取得1或是0的值
    let carry = 0;
    
    // while (l1 != null || l2 != null || carry != 0)
    while (l1 || l2 || carry) {
        let sum = carry;
        if (l1) {
            sum += l1.val;
            l1 = l1.next;
        }
        if (l2) {
            sum += l2.val;
            l2 = l2.next;
        }
        if (sum >= 10) {
        // 如果總和是2位數，將carry=1帶到下一次迴圈
            carry = 1;
            sum -= 10;
        } else {
            carry = 0;
        }
        // 將新的節點代入解答中
        currNode.next = new ListNode(sum);
		
        // 推進當前的節點
        currNode = currNode.next;
    }
    
    return headNode.next;  
};


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*新手工程師的筆記，純粹記錄學了些啥東西
如果有前輩高人讀了我的文，文中有任何錯誤再麻煩指教指教*