leetcode 2|455. Add Two Numbers 1|2

两数相加算法实现

最新推荐文章于 2021-12-02 14:05:46 发布

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本文介绍了两种不同的链表形式下实现两个非负整数相加的方法。第一种方法中，链表节点按逆序存储数字；第二种方法则按正序存储。针对每种情况，文章提供了详细的算法思路及C++代码实现。

2. Add Two Numbers

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) 
    {
        int flag = 0;
        ListNode result(1); 
        if (l1 == NULL)
            return l2;
        if (l2 == NULL)
            return l1;
        ListNode* p = &result;
        while (l1 && l2)
        {
            ListNode * NewNode = new ListNode((l1->val + l2->val + flag) % 10);   
            p->next = NewNode;
            p = p->next;
            flag = (l1->val + l2->val + flag) / 10;
            l1 = l1->next;
            l2 = l2->next;
        }
        if (flag == 0)
        {
            if (l1)
                p->next = l1;
            if (l2)
                p->next = l2;  
        }
        else
        {
            ListNode * NewNode = new ListNode(1);
            if (l1)
                p->next = addTwoNumbers(l1, NewNode);
            else if (l2)
                p->next = addTwoNumbers(l2, NewNode);  
            else
                p->next = addTwoNumbers( NULL, NewNode); 
        }
        return result.next; 
    }
};

445. Add Two Numbers II

You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Follow up:
What if you cannot modify the input lists? In other words, reversing the lists is not allowed.

Example:

Input: (7 -> 2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 8 -> 0 -> 7

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) 
    {
        stack<int> sk1;
        while (l1)
        {
            sk1.push(l1->val);
            l1 = l1->next;
        }
        
        stack<int> sk2;
        while (l2)
        {
            sk2.push(l2->val);
            l2 = l2->next;
        }
        
        int flag = 0;
        ListNode* last = NULL;
        while (!sk1.empty() || !sk2.empty())
        {
            int v1 = 0;
            if (!sk1.empty())
            {
                v1 = sk1.top();
                sk1.pop();
            }
            int v2 = 0;
            if (!sk2.empty())
            {
                v2 = sk2.top();
                sk2.pop();   
            }
            ListNode* now = new ListNode( (v1 + v2 + flag) % 10 );
            //cout<<v1<<" "<<v2<<" "<<now->val<<endl;
            flag = (v1 + v2 + flag) / 10;
            now->next = last;
            last = now;
        }
        if (flag)
        {
            ListNode* now = new ListNode( 1 );
            now->next = last;
            return now;
        }
        return last;
    }
};