What is the difference between Vec and VecDeque

Vec is a growable array optimized for fast access and appending at the end, while VecDeque is a double-ended queue optimized for fast insertion and removal at both the front and back. Use Vec for standard lists and VecDeque when you need a queue or stack that operates efficiently on both ends.

use std::collections::VecDeque;

// Vec: Fast push/pop at the end
let mut v = Vec::new();
v.push(1);
let last = v.pop(); // Removes from end

// VecDeque: Fast push/pop at both ends
let mut dq = VecDeque::new();
dq.push_front(1); // Fast at front
dq.push_back(2);  // Fast at back
let first = dq.pop_front(); // Removes from front

Think of a Vec as a standard shopping list where you only add or remove items from the bottom. A VecDeque is like a line at a ticket counter where people can join or leave from either the front or the back. You choose Vec for simple lists and VecDeque when you need to process items from both ends quickly.