Home
Algorithms Data Structures Interview Experiences
Amazon Google Facebook Microsoft Apple Netflix
Play 2048 How to

LeetCode Solutions

382. Linked List Random Node

Time: $O(n)$

Space: $O(1)$

			


class Solution {
 public:
  /** @param head The linked list's head.
      Note that the head is guaranteed to be not null, so it contains at least
     one node. */
  Solution(ListNode* head) : head(head) {}

  /** Returns a random node's value. */
  int getRandom() {
    int ans = -1;
    int i = 1;

    for (ListNode* curr = head; curr; curr = curr->next, ++i)
      if (rand() % i == 0)
        ans = curr->val;

    return ans;
  }

 private:
  ListNode* head;
};




			


class Solution {
  /**
   * @param head The linked list's head. Note that the head is guaranteed to be
   *             not null, so it contains at least one node.
   */
  public Solution(ListNode head) {
    this.head = head;
  }

  /** Returns a random node's value. */
  public int getRandom() {
    int ans = -1;
    int i = 1;

    for (ListNode curr = head; curr != null; curr = curr.next, ++i)
      if (rand.nextInt(i) == i - 1)
        ans = curr.val;

    return ans;
  }

  private ListNode head;
  private Random rand = new Random();
}