題目連結: https://leetcode.com/problems/plus-one-linked-list/

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

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

思路: 只要用一個遞迴從後往前處理即可, 在最後一個位+1, 然後返回進位值.

程式碼如下:

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    int DFS(ListNode* head)
    {
        int flag = 0;
        if(!head->next) flag = 1;
        else flag = DFS(head->next);
        int val = head->val+flag;
        head->val = val%10;
        flag = val/10;
        return flag;
    }
    
    ListNode* plusOne(ListNode* head) {
        if(!head) return head;
        if(DFS(head)==0) return head;
        ListNode* p = new ListNode(1);
        p->next = head;
        return p;
    }
};