leetcode No369. Plus One Linked List

Posted 2022-06-11 Dufre.WC

Question

Given a non-negative integer represented as non-empty a singly linked list of digits, plus one to the integer.

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

The digits are stored such that the most significant digit is at the head of the list.

Example :

Input: [1,2,3]
Output: [1,2,4]

Algorithm

看的题解，有一个好的思路
最不好处理的是带9的case，比如199 + 1 = 200，这里专门用一个指针记录最早9->0的位置。

• slow，fast两个指针
  • slow：记录9的位置
  • fast：正常遍历的指针
• fast->val等于9的时候，slow不动
• fast->val不等于9的时候，slow移动到fast处
• 遍历结束，slow的值+1，slow后面的都归0

Code

/**
 * Definition for singly-linked list.
 * struct ListNode 
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) 
 * ;
 */
class Solution 
public:
    ListNode* plusOne(ListNode* head) 
        ListNode* slow = new ListNode(0);
        slow->next=head;
        ListNode* fast = head;

        while(fast)
            if (fast->val != 9)
                slow = fast;
            
            fast = fast->next;
              
        slow->val += 1; 
        ListNode* tmp = slow->next;
        while(tmp)
            tmp->val = 0;
            tmp = tmp->next;
        
        return slow->next==head?slow:head;
    
;

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