Mutable borrow occurs here [E0502] - rust

Question

How can I correct this behavior ?
P.S Now I am trying to implement a search for the number of page_faults when using the FIFO algorithm
fn page_fault(capacity: i32, n: i32, pages: &[i32]) -> i32 {
let mut s: HashSet<i32> = HashSet::new();
let mut indexes: VecDeque<i32> = VecDeque::new();
let mut page_faults: i32 = 0;
for i in 0..n {
if (s.len() as i32) < capacity {
if s.contains(&pages[(i) as usize]) {
s.insert(pages[(i) as usize]);
page_faults += 1;
indexes.insert(i as usize, pages[(i) as usize])
}
}
else {
if s.contains(&pages[(i) as usize]) {
let val = indexes.front();
indexes.pop_front();
s.remove(&val.unwrap());
s.insert(pages[(i) as usize]);
indexes.push_back(pages[(i) as usize]);
page_faults += 1;
}
}
}
return page_faults;
}
Terminal:
let val = indexes.front();
--------------- immutable borrow occurs here
indexes.pop_front();
^^^^^^^^^^^^^^^^^^^ mutable borrow occurs here
s.remove(&val.unwrap());
--- immutable borrow later used here

Answer 1

Calling indexes.front() seems redundant to me. You can simply use the result of indexes.pop_front() and assign it to a variable. So you can replace these two lines:
let val = indexes.front();
indexes.pop_front();
With this line:
let val = indexes.pop_front();

Answer 2

When calling indexes.front you are keeping a reference to it (&self), it can be easily solved by unwraping inmediatly and dereferencing it so the i32 is copied. Then the reference is freed.
use std::collections::VecDeque;
use std::collections::HashSet;
fn page_fault(capacity: i32, n: i32, pages: &[i32]) -> i32 {
let mut s: HashSet<i32> = HashSet::new();
let mut indexes: VecDeque<i32> = VecDeque::new();
let mut page_faults: i32 = 0;
for i in 0..n {
if (s.len() as i32) < capacity {
if s.contains(&pages[(i) as usize]) {
s.insert(pages[(i) as usize]);
page_faults += 1;
indexes.insert(i as usize, pages[(i) as usize])
}
}
else {
if s.contains(&pages[(i) as usize]) {
let val = *indexes.front().unwrap();
indexes.pop_front();
s.remove(&val);
s.insert(pages[(i) as usize]);
indexes.push_back(pages[(i) as usize]);
page_faults += 1;
}
}
}
return page_faults;
}
Playground