Added day09 solutions

2016/day09/src/main.rs

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+extern crate regex;
+
+use regex::Regex;
+use std::io::Read;
+use std::fs::File;
+
+fn part_1(input: &String) {
+    let set: Vec<char> = input.chars().collect();
+    let mut idx: usize = 0;
+    let mut output = String::new();
+    let re = Regex::new(r"\((\d+)x(\d+)\)").unwrap();
+    //step by single characters
+    //when you find an open paren, look for the next closing paren and match to a regex like (x,y)
+    //if it does not match, add contents to output and continue
+    //if it matches, add the next 'x' characters to the output 'y' times and increase idx by 'x'
+    //if not an open paren, add to output
+    while idx < input.len() {
+        let c = set[idx];
+        match c {
+            '(' => {
+                let old_idx: usize = idx; //for when we have to colleect the slice
+                loop {
+                    idx = idx + 1;
+                    match set[idx] {
+                        ')' => break,
+                        _ => {},
+                    }
+                }
+                let cap_slice = &input[old_idx..idx+1];
+                let cap = re.captures(cap_slice).unwrap();
+
+                let char_count: usize = cap.at(1).unwrap().parse().unwrap();
+                let times = cap.at(2).unwrap().parse().unwrap();
+
+                print!("({}x{}) ", char_count, times);
+                //println!("({}x{}) adding slice from {} to {}", char_count, times, idx, idx+char_count);
+                for time in 0..times {
+                    output = output + &input[idx+1..idx+char_count+1]; //copy the next char_count characters
+                }
+                idx = idx + char_count; //skip over all the chars we added
+
+            },
+            _ => {
+                output.push(c);
+                //println!("{} input is len {}", idx, input.len());
+                },
+        }
+        idx = idx + 1; //increment idx in every case
+    }
+    println!("Final size is {}", output.len());
+}
+
+fn get_count(input: &String) -> usize {
+    let re_letters = Regex::new(r"^[^\(\)]*$").unwrap(); //I'd prefer to make this static but don't know how
+    if re_letters.is_match(&input) { //if there are no parens
+        return input.len(); //return the length
+    }
+    let re = Regex::new(r"^([:alpha:]*)\((\d+)x(\d+)\)(.*)$").unwrap();
+    match re.captures(input) {
+        None => println!("Found nothing!"),
+        Some(cap) => {
+            let letters = cap.at(1).unwrap().to_string();
+            let count: usize = cap.at(2).unwrap().parse().unwrap();
+            let times: usize = cap.at(3).unwrap().parse().unwrap();
+            let subslice = &cap.at(4).unwrap()[0..count].to_string();
+            let therest = &cap.at(4).unwrap()[count..].to_string();
+
+            //println!("Found: {} - {},{}", cap.at(1).unwrap(), cap.at(2).unwrap(), cap.at(3).unwrap()),
+            println!("({},{}) - {}x {}", count, times, times, subslice);
+            return get_count(&letters) + times * get_count(subslice) + get_count(therest);
+        }
+    }
+    0
+}
+
+fn part_2(input: &String) {
+    println!("Part 2: Length is {}", get_count(input));
+}
+
+fn main() {
+    let mut file = File::open("./data").expect("could not open file");
+    let mut input = String::new();
+    file.read_to_string(&mut input).expect("could not read file");
+
+    //part_1(&input);
+    part_2(&input);
+}