【LeetCode-剑指offer】-- 25.两数相加II

25.两数相加II

方法：栈

/**
 * 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) {
   
        Stack<Integer> stack1 = new Stack<Integer>();
        Stack<Integer> stack2 = new Stack<Integer>();
        while(l1!=null){
   
            stack1.push(l1.val);
            l1 = l1.next;
        }
        while(l2!=null){
   
            stack2.push(l2.val);
            l2 = l2.next;
        }
        int carry = 0;
        ListNode ans = null;
        while(!stack1.isEmpty() || !stack2.isEmpty() || carry != 0){
   
            int a = stack1.isEmpty() ? 0 : stack1.pop();
            int b = stack2.isEmpty() ? 0 : stack2.pop();
            int cur = a + b + carry;
            carry = cur / 10;
            cur %= 10;
            //头插法
            ListNode curNode = new ListNode(cur);
            curNode.next = ans;
            ans = curNode;
        }
        return ans;
    }
}