题解 | #链表相加(二)#

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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 static ListNode reverse(ListNode node){
        ListNode pre = null;
        ListNode next = null;
        
        while(node!=null){
            next = node.next;
            node.next=pre;
            pre = node;
            node = next;
        }
        return pre;
    }
    
    public ListNode addInList (ListNode head1, ListNode head2) {
        // write code here
        ListNode l1 = reverse(head1);
        ListNode l2 = reverse(head2);
        
        Stack<Integer> s = new Stack<>();
        
        int j = 0;
        int sum = 0;
        while(l1!=null||l2!=null){
            if(l1!=null){
                sum=sum+l1.val;
                l1=l1.next;
            }
            if(l2!=null){
                sum=sum+l2.val;
                l2=l2.next;
            }
            sum=sum+j;
            int res = sum%10;
            s.add(res);    
            if(sum>=10){
                j=1;
            }else{
                j=0;
            }  
            sum=0;
        }
        if(j==1){
            s.add(1);
        }
        
        ListNode head;
        ListNode node = new ListNode(s.pop());
        head = node;
        while(!s.isEmpty()){
            ListNode nextnode = new ListNode(s.pop());
            node.next=nextnode;
            node = node.next;
        }
        
        return head;

    }
}