382. 链表随机节点

蓄水池算法随机抽样视频参考

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    ListNode head;
    int count = 0;
    Random random;
    public Solution(ListNode head) {
        this.head = head;
        random = new Random();

    }
    
    public int getRandom() {
       int res = 0;
       int count = 0;
       ListNode cur = head;
       while (cur != null) {
           count++;
           int r = random.nextInt(count) + 1;
           if (r == count) {
               res = cur.val;
           }
           cur = cur.next;
       }
       return res;
    }
}

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