find the largest value in a map in rust

To find the largest value in a map in Rust, we can use the max_by_key function provided by the standard library. Here's an example:

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

fn main() {
    let mut map = HashMap::new();
    map.insert("a", 1);
    map.insert("b", 2);
    map.insert("c", 3);
    
    if let Some(max_value) = map.values().max_by_key(|&&v| v) {
        println!("The maximum value in the map is: {}", max_value);
    }
}
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In this example, we create a new HashMap and insert some values into it. Then, we use the max_by_key function to find the maximum value in the map. The max_by_key function takes a closure that maps each value in the map to a key, and returns the maximum key according to the natural ordering of keys. In our example, we use a closure that simply returns the value itself, since we want to find the maximum value.

Note that the max_by_key function returns an Option since it's possible for the map to be empty. We use a match statement (if let in this case) to handle the Some case and print the maximum value.