CodingQuestion/src/LeetCode-2-Add-Two-Numbers.java at master · drinkbeer/CodingQuestion · GitHub

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/*
LeetCode: https://leetcode.com/problems/add-two-numbers/
LintCode: http://www.lintcode.com/problem/add-two-numbers/
JiuZhang: http://www.jiuzhang.com/solutions/add-two-numbers/
ProgramCreek: http://www.programcreek.com/2012/12/add-two-numbers/

Analysis:
Building a new list to store the result. Using a dummy node to record the pre-node of head in new list. Curr node to record the current pos.
Be careful: the last add of last two node may generate a '1', which need a new node.

*/
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
//     public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
//         if(l1 == null || l2 == null) return null;

//         ListNode dummy = new ListNode(0);
//         ListNode curr = dummy;
//         ListNode p1 = l1, p2 = l2;

//         int carry = 0;

//         while(p1 != null || p2 != null){

//             if(p1 != null){
//                 carry += p1.val;
//                 p1 = p1.next;
//             }

//             if(p2 != null){
//                 carry += p2.val;
//                 p2 = p2.next;
//             }

//             curr.next = new ListNode(carry % 10);
//             carry = carry / 10;
//             curr = curr.next;
//         }

//         if(carry == 1){
//             curr.next = new ListNode(1);
//             curr = curr.next;
//         }

//         return dummy.next;
//     }


//     public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
//         int carry = 0;
//         ListNode dummy = new ListNode(-1);
//         ListNode p = dummy;

//         while(l1 != null && l2 != null) {
//             int temp = carry;
//             carry = (l1.val + l2.val + temp) / 10;
//             ListNode curr = new ListNode((l1.val + l2.val + temp) % 10);
//             p.next = curr;
//             p = p.next;
//             l1 = l1.next;
//             l2 = l2.next;
//         }

//         while (l1 != null) {
//             int temp = carry;
//             carry = (l1.val + temp) / 10;
//             ListNode curr = new ListNode((l1.val + temp) % 10);
//             p.next = curr;
//             p = p.next;
//             l1 = l1.next;
//         }

//         while (l2 != null) {
//             int temp = carry;
//             carry = (l2.val + temp) / 10;
//             ListNode curr = new ListNode((l2.val + temp) % 10);
//             p.next = curr;
//             p = p.next;
//             l2 = l2.next;
//         }

//         if (carry != 0) {
//             ListNode curr = new ListNode(carry);
//             p.next = curr;
//         }

//         return dummy.next;
//     }

    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        int carry =  0;
        ListNode dummy = new ListNode(-1);
        ListNode pre = dummy;

        while(l1 != null && l2 != null) {
            int val = (l1.val + l2.val + carry) % 10;
            carry = (l1.val + l2.val + carry) / 10;
            pre.next = new ListNode(val);

            l1 = l1.next;
            l2 = l2.next;
            pre = pre.next;
        }

        while (l1 != null) {
            int val = (l1.val + carry) % 10;
            carry = (l1.val + carry) / 10;
            pre.next = new ListNode(val);

            l1 = l1.next;
            pre = pre.next;
        }

        while(l2 != null) {
            int val = (l2.val + carry) % 10;
            carry = (l2.val + carry) / 10;
            pre.next = new ListNode(val);

            l2 = l2.next;
            pre = pre.next;
        }

        if (carry != 0) pre.next = new ListNode(carry);

        return dummy.next;
    }

}