题解 | #两个链表生成相加链表#

一个比较捞的方法。。
求改进

public ListNode addInList (ListNode head1, ListNode head2) {
        int carry = 0;//进位符
        ListNode h1 = reverseList(head1);//链表反转
        ListNode h2 = reverseList(head2);//链表反转
        //遍历定长部分
        ListNode l1 = h1;
        ListNode l2 = h2;
        int len1 = 0,len2 = 0;
        while(l1 != null){
            len1++;
            l1 = l1.next;
        }
        while(l2 != null){
            len2++;
            l2 = l2.next;
        }

        ListNode ans = new ListNode(-1);//结果链表
        if(len1>=len2){
            ans.next = head1;
        }else{
            ans.next = head2;
        }//结果链表定长为较长的一个+1

        ListNode f1 = h1;
        ListNode f2 = h2;//f1和f2双指针用来做加法
        ListNode tmp = ans;//创建指针在结果链表上移动
        while(f1 != null || f2 != null || carry!=0){
            int x=0,y=0;
            if(f1 != null){
                x=f1.val;
                f1=f1.next;
            }
            if(f2 !=null){
                y=f2.val;
                f2=f2.next;
            }
            int sum = x+y+carry;
            tmp.val = sum%10;
            tmp = tmp.next;
            carry = sum/10;
            if(carry==0 && f1 == null && f2==null){
                ans = reverseList(ans); //如果全为0，不计算最后一位，反转输出链表.next
                return ans.next;
            }
        }
        ans = reverseList(ans);
        return ans;
    }
    //链表反转
    public ListNode reverseList(ListNode head){
        if(head == null || head.next == null){
            return head;
        }
        Stack<Integer> stack = new Stack<Integer>();
        ListNode temp = head;
        while(temp != null){
            stack.push(temp.val);
            temp = temp.next;
        }
        ListNode cur = head;
        while(!stack.isEmpty()){
            cur.val = stack.pop();
            cur = cur.next;
        }
        return head;
    }