LeetCode 1146. Snapshot Array

Problem Statement

use std::collections::{HashMap, BTreeMap};

struct SnapshotArray {
    map : HashMap<i32, BTreeMap<i32, i32>>,
    version: i32
}

/**
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl SnapshotArray {

    fn new(length: i32) -> Self {
        SnapshotArray {
            map: HashMap::new(),
            version: 0
        }
    }

    fn set(&mut self, index: i32, val: i32) {
        self.map.entry(index).or_insert(BTreeMap::new());
        self.map.get_mut(&index).unwrap().insert(self.version, val);
    }

    fn snap(&mut self) -> i32 {
        let ret = self.version;
        self.version += 1;
        return ret;
    }

    fn get(&self, index: i32, snap_id: i32) -> i32 {
        if !self.map.contains_key(&index) {
            return 0;
        }
        let vals = self.map.get(&index).unwrap();
        let mut ans = 0;
        for entry in vals {
            if snap_id >= *entry.0 {
                ans = *entry.1;
            } else {
               break;
            }
        }
        return ans;
    }
}