Leetcode_0002_AddTwoNumbers 两数相加 中等

public class Leetcode_0002_AddTwoNumbers {

    public static class ListNode {
        int val;
        ListNode next;

        ListNode() {
        }

        ListNode(int val) {
            this.val = val;
        }

        ListNode(int val, ListNode next) {
            this.val = val;
            this.next = next;
        }
    }

    public static ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        // 参数清洗
        if (l1 == null && l2 == null) {
            return null;
        }
        if (l1 == null) {
            return l2;
        }
        if (l2 == null) {
            return l1;
        }
        // 新的头
        ListNode preHead = new ListNode(-1);
        // 进位 cp
        int cp = 0;
        int val1 = 0;
        int val2 = 0;
        int cur = 0;
        ListNode curNode = preHead;
        while (l1 != null || l2 != null) {
            val1 = l1 == null ? 0 : l1.val;
            val2 = l2 == null ? 0 : l2.val;
            cur = val1 + val2 + cp;
            curNode.next = new ListNode(cur % 10);
            cp = cur / 10;
            l1 = l1 == null ? l1 : l1.next;
            l2 = l2 == null ? l2 : l2.next;
            curNode = curNode.next;
        }
        // 处理进位 cp
        if (cp > 0) {
            curNode.next = new ListNode(cp);
        }
        return preHead.next;
    }

    public static void main(String[] args) {
        var l1 = new ListNode(1); // 1 -> 9 -> 9
        l1.next = new ListNode(9);
        l1.next.next = new ListNode(9);

        var l2 = new ListNode(1); // 1 -> 9
        l2.next = new ListNode(9);

        // 2-> 8 -> 0 -> 1
        var head = addTwoNumbers(l1, l2);

        while (head != null) {
            System.out.print(head.val + "-> ");
            head = head.next;
        }
    }
}