466. Count Linked List Nodes【Naive】

Count how many nodes in a linked list.

Example

Given 1->3->5, return 3.

解法一：

/**
 * Definition of ListNode
 * class ListNode {
 * public:
 *     int val;
 *     ListNode *next;
 *     ListNode(int val) {
 *         this->val = val;
 *         this->next = NULL;
 *     }
 * }
 */


class Solution {
public:
    /*
     * @param head: the first node of linked list.
     * @return: An integer
     */
    int countNodes(ListNode * head) {
        if (head == NULL) {
            return 0;
        } else if (head->next == NULL) {
            return 1;
        }
        
        return 1 + countNodes(head->next);
    }
};

递归

解法二：

/**
 * Definition of ListNode
 * class ListNode {
 * public:
 *     int val;
 *     ListNode *next;
 *     ListNode(int val) {
 *         this->val = val;
 *         this->next = NULL;
 *     }
 * }
 */


class Solution {
public:
    /*
     * @param head: the first node of linked list.
     * @return: An integer
     */
    int countNodes(ListNode * head) {
        if (head == NULL) {
            return 0;
        } 
        
        int sum = 0;
        while (head != NULL) {
            ++sum;
            head = head->next;
        }
        
        return sum;
    }
};