Add Two Numbers

ID: 2; medium

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Solution 1 (Go)

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func addTwoNumbers(l1 *ListNode, l2 *ListNode) *ListNode {
    head := &ListNode{Val: 0}   // dummy node
    val1, val2, carry, runner := 0, 0, 0, head
    for l1 != nil || l2 != nil || carry == 1 {
        if l1 == nil {
            val1 = 0
        } else {
            val1 = l1.Val
            l1 = l1.Next
        }
        if l2 == nil {
            val2 = 0
        } else {
            val2 = l2.Val
            l2 = l2.Next
        }
        runner.Next = &ListNode{Val: (val1 + val2 + carry) % 10}
        carry = (val1 + val2 + carry) / 10
        runner = runner.Next
    }
    return head.Next
}

Solution 2 (Java)

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode(0);
        ListNode head = dummy;
        int carry = 0;
        while (l1 != null && l2 != null) {
            int val = (l1.val + l2.val + carry) % 10;
            carry = (l1.val + l2.val + carry) / 10;
            ListNode newNode = new ListNode(val);
            head.next = newNode;
            head = newNode;
            l1 = l1.next;
            l2 = l2.next;
        }
        while (l1 == null && l2 != null)  {
            int val = (l2.val + carry) % 10;
            carry = (l2.val + carry) / 10;
            ListNode newNode = new ListNode(val);
            head.next = newNode;
            head = newNode;
            l2 = l2.next;
        }
        while (l2 == null && l1 != null)  {
            int val = (l1.val + carry) % 10;
            carry = (l1.val + carry) / 10;
            ListNode newNode = new ListNode(val);
            head.next = newNode;
            head = newNode;
            l1 = l1.next;
        }
        if (carry == 1) head.next = new ListNode(1);
        return dummy.next;
    }
}

//     9 -> 9 -> 9 -> 9
//     9 -> 9
//     8 -> 9 -> 0 -> 0 -> 1

Solution 3 (Java)

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode(0);
        ListNode curr = dummy;
        int carry = 0;
        while (l1 != null || l2 != null || carry != 0) {
            int x = (l1 != null) ? l1.val : 0;
            int y = (l2 != null) ? l2.val : 0;
            int sum = x + y + carry;
            carry = sum / 10;
            curr.next = new ListNode(sum % 10);
            curr = curr.next;
            if (l1 != null) l1 = l1.next;
            if (l2 != null) l2 = l2.next;
        }
        return dummy.next;
    }
}

// 1111111
//  9999999
//     9999
// 10009998