leetcode382 链表随机节点

思路：

蓄水池采样。

实现：

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    int len=0;
    ListNode*h=NULL;
    Solution(ListNode* head) {
        h=head;
        while(head){
            len++;
            head=head->next;
        }
    }
    
    int getRandom() {
        int cur=0;
        ListNode*tmp=h;
        for(int i=1;i<=len;i++){
            int num=rand()%i;
            if(num==0)cur=tmp->val;
            tmp=tmp->next;
        }
        return cur;
    }
};

/**
 * Your Solution object will be instantiated and called as such:
 * Solution* obj = new Solution(head);
 * int param_1 = obj->getRandom();
 */