q002_AddTwoNumbers.java

package leetcode_algorithm;

/**
    You are given two linked lists representing two non-negative numbers.
     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.

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

public class q002_AddTwoNumbers {

    public static void main(String[] args) {
        ListNode a1 = new ListNode(2);
        ListNode a2 = new ListNode(4);
        ListNode a3 = new ListNode(3);
        a1.next = a2;
        a2.next = a3;

        ListNode b1 = new ListNode(5);
        ListNode b2 = new ListNode(6);
        ListNode b3 = new ListNode(4);
        b1.next = b2;
        b2.next = b3;

        System.out.println(solution(a1 , a2));
    }

    /**
     * ½â·¨1
     *
     * @param l1
     * @param l2
     * @return
     */
    public static  ListNode solution(ListNode l1 , ListNode l2){
        ListNode dummyHead = new ListNode(0);
        ListNode p = l1 , q = l2 , curr = dummyHead;
        int carry = 0;
        while (p != null || q != null) {
            int x = (p != null) ? p.val : 0;
            int y = (q != null) ? q.val : 0;
            int sum = carry + x + y;
            carry = sum/10;
            curr.next = new ListNode(sum % 10);
            curr = curr.next;
            if (p != null) p = p.next;
            if(q != null) q = q.next;
        }
        if (carry > 0) {
            curr.next = new ListNode(carry);
        }
        return dummyHead.next;
    }

    private static class ListNode {

        int val;

        ListNode next;

        ListNode(int x) {
            val = x;
        }

        public String toString() {
            return val + " " + (next != null ? next : "");
        }

    }

}