Rust updating vector values - vector

Question

I just want to find three largest numbers of an Vec<i32> sorted in ascending order, but I have problem with the last function. I don't know how I should do this properly.
pub struct Solution;
impl Solution {
pub fn find_three_largest_numbers(array: Vec<i32>) -> Vec<i32> {
let mut max_arr = vec![i32::MIN, i32::MIN, i32::MIN];
for number in array {
max_arr = Solution::update_array(max_arr, number);
}
max_arr
}
fn update_array(array: Vec<i32>, number: i32) -> Vec<i32> {
if array[2] < number {
Solution::assign_values(&array, 2, number);
} else if array[1] < number {
Solution::assign_values(&array, 1, number);
} else if array[0] < number {
Solution::assign_values(&array, 0, number);
}
array
}
fn assign_values(array: &Vec<i32>, index: i32, number: i32) {
for i in 0..index+1 {
if i == index {
array[i as usize] = number; // ERROR: `array` is a `&` reference, so the data it refers to cannot be borrowed as mutable
} else {
array[i as usize] = array[(i + 1) as usize]; // ERROR: `array` is a `&` reference, so the data it refers to cannot be borrowed as mutable
}
}
}
}

Answer 1

reference are by default immutable and since you are passing immutable vec reference which can be use to update the vec which is what rust is complaining.
To solve this you have to pass mutable reference which can be use to update the vec.
pub struct Solution;
impl Solution {
pub fn find_three_largest_numbers(array: Vec<i32>) -> Vec<i32> {
let mut max_arr = vec![i32::MIN, i32::MIN, i32::MIN];
for number in array {
max_arr = Solution::update_array(&mut max_arr, number);
}
max_arr
}
fn update_array(array: &mut Vec<i32>, number: i32) -> Vec<i32> {
if array[2] < number {
Solution::assign_values(array, 2, number);
} else if array[1] < number {
Solution::assign_values(array, 1, number);
} else if array[0] < number {
Solution::assign_values(array, 0, number);
}
array.to_vec()
}
fn assign_values(array: &mut Vec<i32>, index: i32, number: i32) {
for i in 0..index + 1 {
if i == index {
array[i as usize] = number;
} else {
array[i as usize] = array[(i + 1) as usize];
}
}
}
}
fn main() {
println!(
"{:?}",
Solution::find_three_largest_numbers(vec![-1, 3, 15, 6, -40])
);
}
Playground
Note: One improvement I would like to suggest since you are passing mutable reference you don't need reassignment to max_arr or return from update_array method.

Answer 2

Here's a little solution I whipped up :) Hope it helps!
(P.S. I made sure not to use fancy iterators, just in case you're new to Rust :))
pub struct Solution;
impl Solution {
pub fn find_three_largest_numbers(array: Vec<i32>) -> Vec<i32> {
let mut largest = vec![];
for a in array.iter() {
if largest.len() < 3 {
largest.push(*a);
} else {
for i in 0..largest.len() {
if a > &largest[i]
&& !largest.contains(a) {
largest[i] = *a;
}
}
}
}
largest
}
}
fn main() {
println!("{:?}", Solution::find_three_largest_numbers(vec![-1, 3, 15, 6, -40]));
}