find the mode of all nodes in a linked list in rust

main.rs
use std::collections::HashMap;

// Define a node struct for the linked list
struct Node {
    value: i32,
    next: Option<Box<Node>>,
}

impl Node {
    fn new(v: i32) -> Self {
        Self { value: v, next: None }
    }
}

fn mode_of_linked_list(head: Option<Box<Node>>) -> Option<i32> {
    if head.is_none() {
        return None;
    }

    let mut map = HashMap::new();

    // Traverse the linked list and count occurrences of each value
    let mut cur = head;
    while let Some(node) = cur {
        let count = map.entry(node.value).or_insert(0);
        *count += 1;
        cur = node.next;
    }

    // Find the mode value
    let mut mode = None;
    let mut max_count = 0;
    for (value, count) in map {
        if count > max_count {
            mode = Some(value);
            max_count = count;
        }
    }

    mode
}

// Example usage
fn main() {
    let n1 = Node::new(1);
    let n2 = Node::new(2);
    let n3 = Node::new(3);
    let n4 = Node::new(2);

    n1.next = Some(Box::new(n2));
    n2.next = Some(Box::new(n3));
    n3.next = Some(Box::new(n4));

    let mode = mode_of_linked_list(Some(Box::new(n1)));
    println!("Mode of linked list is {:?}", mode); // Mode of linked list is Some(2)
}
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