NC40 两个链表生成相加链表

栈

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param head1 ListNode类 
     * @param head2 ListNode类 
     * @return ListNode类
     */
    public ListNode addInList (ListNode head1, ListNode head2) {
        Stack<Integer> num1 = new Stack<>();
        Stack<Integer> num2 = new Stack<>();

        for(ListNode i = head1; i!=null;i=i.next) num1.push(i.val);
        for(ListNode i = head2; i!=null;i=i.next) num2.push(i.val);

        int add1 = 0; 
        int count = 0;
        ListNode sumhead = new ListNode(0);

        while(!num1.empty() || !num2.empty() || add1 ==1){
            int dig1 = num1.empty()?0:num1.pop();
            int dig2 = num2.empty()?0:num2.pop();

            int cursum = dig1 + dig2 + add1;
            ListNode temp = new ListNode(cursum%10);
            temp.next = sumhead.next;
            sumhead.next = temp;

            if(dig1 + dig2 + add1  >9) add1 = 1;
            else add1 = 0;
        }
        return sumhead.next;
    }
}

反转链表
注意最后一位 都为空的时候 也有可能得到后面数组的进位。所以也要判断一下

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param head1 ListNode类 
     * @param head2 ListNode类 
     * @return ListNode类
     */
    public ListNode addInList (ListNode head1, ListNode head2) {
        head1 = reverseList(head1);
        head2 = reverseList(head2);

        ListNode sumhead = new ListNode(0);
        int ifadd = 0;
        while(head1!=null || head2!=null){
            ListNode temp = sumhead.next;
            int res;
            if(head1 == null){
                res = head2.val + ifadd;
            }else if(head2 == null){
                res = head1.val + ifadd;
            }else{
                res = head1.val + head2.val + ifadd;
            }
            if(res >= 10){
                res = res%10;
                ifadd = 1;
            }
            else{ ifadd = 0;}
            sumhead.next = new ListNode(res);
            sumhead.next.next = temp;

            if(head1!=null) head1 = head1.next;
            if(head2!=null) head2 = head2.next;
        }
        if(ifadd == 1){
            ListNode temp = sumhead.next;
            sumhead.next = new ListNode(1);
            sumhead.next.next = temp;
        }

        return sumhead.next;
    }

    public ListNode reverseList(ListNode head){
        ListNode cur = head;
        ListNode prev = null;
        while(cur!=null){
            ListNode temp = cur.next;
            cur.next = prev;
            prev = cur;
            cur = temp;
        }
        return prev;
    }
}