2. Add Two Numbers

2. Add Two Numbers

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 contain a single digit. Add the two numbers and return it as a linked list.

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

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

 

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var addTwoNumbers = function(l1, l2) {
    
    //这种累加的题目，主要是注意进位
    var carry = 0;
    //头指针
    var head = new ListNode(0);

    var res = head;
    
    //保证两个都有值 就累加，否者就直接添加
    while(l1&&l2){
        
        //一开始就加上carry,默认是0
        var val = l1.val + l2.val + carry;
        val - 9 > 0 ? carry = 1 : carry = 0;
     
        val %= 10;  
        var node = new ListNode(val);
        res.next = node;
        
        res = node;
        
        l1 = l1.next;
        l2 = l2.next;
       
    }
    
    //处理 2->3->4 + 2->3 这种
    while(l1){
     
            var val = l1.val + carry;
            val - 9 > 0 ? carry = 1 : carry = 0;
            val %= 10;
            var node = new ListNode(val);
            res.next = node;
        
            res = node;
            l1 = l1.next;
     
    }
    
     while(l2){
     
            var val = l2.val + carry;
            val - 9 > 0 ? carry = 1 : carry = 0;
            val %= 10;
            var node = new ListNode(val);
            res.next = node;
        
            res = node;
            l2 = l2.next;
    }
    
    //注意处理最后一个进位  比如 5,5  输出0->1
    if(carry){
           var node = new ListNode(carry);
            res.next = node;

            res = node;
    }
    
    return head.next;
    
    
};