Rust solution for the 2016 Advent of Code Day 1, parts 1 and 2. My original solution was in Java, but thought I'd give Rust a try.

aoc-day1.rs

// Advent of Code 2016: Day 1
// http://adventofcode.com/2016/day/1

// Data structure representing the elf navigating the city.
struct Elf {
    x:          i32,
    y:          i32,
    heading:    f32,
    positions:  Vec<(i32,i32)>,
    revisit:    bool
}

// Methods for the Elf
impl Elf {

    // Return a tuple representing the Elf's current position
    fn position(&self) -> (i32, i32) {
        (self.x, self.y)
    }

    // Update the elf's heading and move to the new location
    fn turn_left(&mut self, units: i32) {
        self.heading = self.heading + ninety_degrees();
        self.move_units(units);
    }

    // Update the elf's heading and move to the new location
    fn turn_right(&mut self, units: i32) {
        self.heading = self.heading - ninety_degrees();
        self.move_units(units);
    }

    // Move a specified number of blocks in the correct heading
    fn move_units(&mut self, units: i32) {
        for _ in 0..units {
            self.x = self.x + self.heading.cos().round() as i32;
            self.y = self.y + self.heading.sin().round() as i32;
            self.check_location();
            self.update_postion();
        }
    }

    // Calculate the "Taxicab geometry" for the elf:
    // https://en.wikipedia.org/wiki/Taxicab_geometry
    fn taxicab_distance(&mut self) -> i32 {
        self.x.abs() + self.y.abs()
    }

    // Check to see if the elf has been in this location before (needed for part 2)
    fn check_location(&mut self) {
        let position = self.position();
        if self.revisit == false && self.positions.contains(&position) {
            println!("The first time the elf visits a location twice, it is at a taxicab distance of {} (part 2).", self.taxicab_distance());
            self.revisit = true
        }
    }

    // Add the current position to the list of places the elf has visited
    fn update_postion(&mut self) {
        let position = self.position();
        self.positions.push(position);
    }
}

// Helper method for proper orientation. Keeps the code clean
fn ninety_degrees() -> f32 {
    use std::f32;
    f32::consts::PI / 2.0
}

// Helper method for determining how many units the elf will travel
fn get_units(direction: &str) -> i32 {
    direction[1..].parse::<i32>().unwrap()
}

fn main() {

    // Initialize the elf
    let mut elf = Elf { x: 0, y: 0, heading: ninety_degrees(), positions: Vec::new(), revisit: false };

    // Input from AoC
    let input = "L1, R3, R1, L5, L2, L5, R4, L2, R2, R2, L2, R1, L5, R3, L4, L1, L2, R3, R5, L2, R5, L1, R2, L5, R4, R2, R2, L1, L1, R1, L3, L1, R1, L3, R5, R3, R3, L4, R4, L2, L4, R1, R1, L193, R2, L1, R54, R1, L1, R71, L4, R3, R191, R3, R2, L4, R3, R2, L2, L4, L5, R4, R1, L2, L2, L3, L2, L1, R4, R1, R5, R3, L5, R3, R4, L2, R3, L1, L3, L3, L5, L1, L3, L3, L1, R3, L3, L2, R1, L3, L1, R5, R4, R3, R2, R3, L1, L2, R4, L3, R1, L1, L1, R5, R2, R4, R5, L1, L1, R1, L2, L4, R3, L1, L3, R5, R4, R3, R3, L2, R2, L1, R4, R2, L3, L4, L2, R2, R2, L4, R3, R5, L2, R2, R4, R5, L2, L3, L2, R5, L4, L2, R3, L5, R2, L1, R1, R3, R3, L5, L2, L2, R5";

    // Split the input into a list of directions
    let directions = input.split(", ");

    // Process the directions
    for dir in directions {
        let units = get_units(dir);
        if dir.starts_with("L") {
            elf.turn_left(units);
        }
        else {
            elf.turn_right(units);
        }
    }

    // Tell us where the elf ended up
    println!("The elf ends up {} taxicab blocks away (part 1).",
        elf.taxicab_distance()
    );

}