src/bin/linked-list-random-node.rs

Author: bestgopher

src/bin/linked-list-random-node.rs

@@ -0,0 +1,59 @@
+use rand::Rng;
+
+fn main() {}
+
+// Definition for singly-linked list.
+#[derive(PartialEq, Eq, Clone, Debug)]
+pub struct ListNode {
+    pub val: i32,
+    pub next: Option<Box<ListNode>>,
+}
+
+impl ListNode {
+    #[inline]
+    fn new(val: i32) -> Self {
+        ListNode {
+            next: None,
+            val,
+        }
+    }
+}
+
+/**
+ * Your Solution object will be instantiated and called as such:
+ * let obj = Solution::new(head);
+ * let ret_1: i32 = obj.get_random();
+ */
+struct Solution {
+    head: Option<Box<ListNode>>
+}
+
+
+/**
+ * `&self` means the method takes an immutable reference.
+ * If you need a mutable reference, change it to `&mut self` instead.
+ */
+impl 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. */
+    fn new(head: Option<Box<ListNode>>) -> Self {
+        Self { head }
+    }
+
+    /** Returns a random node's value. */
+    fn get_random(&self) -> i32 {
+        use rand::Rng;
+        let mut s = &self.head;
+        let mut n = 1;
+        let mut r = 0;
+        while let Some(x) = s {
+            if rand::thread_rng().gen_range(0..n) == 0 {
+                r = x.val;
+            }
+
+            s = &x.next;
+            n += 1;
+        }
+        r
+    }
+}