lintcode(221)連結清單求和 II

Description:

假定用一個連結清單表示兩個數，其中每個節點僅包含一個數字。假設這兩個數的數字順序排列，請設計一種方法将兩個數相加，并将其結果表現為連結清單的形式。

Explanation:

給出 6->1->7 + 2->9->5。即，617 + 295。

傳回 9->1->2。即，912 。

Solution:

利用棧的先進後出，記錄兩個連結清單的節點值。然後計算對應位置的兩個數字之和，如果有進位，指派給flag并帶入下一個計算。

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;      
 *     }
 * }
 */
public class Solution {
    /**
     * @param l1: the first list
     * @param l2: the second list
     * @return: the sum list of l1 and l2 
     */
    public ListNode addLists2(ListNode l1, ListNode l2) {
        // write your code here
        Stack<Integer> temp1 = reverseNode(l1);
        Stack<Integer> temp2 = reverseNode(l2);
        ListNode point = new ListNode(0);
        int flag = 0;
        while((!temp1.isEmpty()) && (!temp2.isEmpty())){
            int value = temp1.pop() + temp2.pop() + flag;
            flag = value/10;
            value = value%10;
            ListNode cur = new ListNode(value);
            cur.next = point.next;
            point.next = cur;
        }
        while(!temp1.isEmpty()){
            int value = temp1.pop() + flag;
            flag = value/10;
            value = value%10;
            ListNode cur = new ListNode(value);
            cur.next = point.next;
            point.next = cur;
        }
        while(!temp2.isEmpty()){
            int value = temp2.pop() + flag;
            flag = value/10;
            value = value%10;
            ListNode cur = new ListNode(value);
            cur.next = point.next;
            point.next = cur;
        }
        if(flag == 1){
            ListNode cur = new ListNode(1);
            cur.next = point.next;
            point.next = cur;
        }
        return point.next;
    }
    
    public Stack<Integer> reverseNode(ListNode temp){
        Stack<Integer> record = new Stack<Integer>();
        while(temp != null){
            record.push(temp.val);
            temp = temp.next;
        }
        return record;
    }
}