Solve day5

1 files changed, 114 insertions, 0 deletions

diff --git a/day5/src/main.rs b/day5/src/main.rs
new file mode 100644
index 0000000..4b2b0bc
--- /dev/null
+++ b/day5/src/main.rs
@@ -0,0 +1,114 @@
+use std::env;
+use std::io::BufReader;
+use std::io::BufRead;
+use std::fs::File;
+use std::process;
+
+static ASCII_LOWER: [char; 26] = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i',
+                                  'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r',
+                                  's', 't', 'u', 'v', 'w', 'x', 'y', 'z'];
+
+fn same_unit(a: &char, b: &char) -> bool {
+  a.to_lowercase().to_string() == b.to_lowercase().to_string()
+}
+
+fn same_polarity(a: &char, b: &char) -> bool {
+  (a.is_lowercase() && b.is_lowercase()) || (a.is_uppercase() && b.is_uppercase())
+}
+
+fn find_removable_indices(chars: &Vec<char>) -> Option<(usize, usize)> {
+  let mut res: Option<(usize, usize)> = None;
+  for (i, cur) in chars.iter().enumerate() {
+    if i == chars.len() - 1 {  // last element
+      break;
+    }
+
+    let next = chars[i + 1];
+    if same_unit(&cur, &next) && !same_polarity(&cur, &next) {
+      res = Some((i, i + 1));
+      break;
+    }
+  }
+
+  res
+}
+
+fn react_polymer(line: &String) -> String {
+  let mut string: Vec<char> = line.trim().chars().collect();
+  loop {
+    let indices = find_removable_indices(&string);
+    let (rem_i1, rem_i2): (usize, usize);
+    match indices {
+      Some((i1, i2)) => {
+        rem_i1 = i1;
+        rem_i2 = i2;
+
+        let s = &mut string;
+        s.remove(rem_i2);
+        s.remove(rem_i1);
+
+        continue;
+      }
+      None => {
+        break;
+      }
+    };
+  }
+
+  string.into_iter().collect()
+}
+
+fn react_polymer_without_char(line: &String, ch: &char) -> String {
+  let line_ref: &str = line.as_ref();
+  let a = *ch;
+  let b_str = a.to_uppercase().to_string();
+  let b: &str = b_str.as_ref();
+  let replaced_line = line_ref.replace(*ch, "").replace(a, "").replace(b, "");
+  let res = react_polymer(&replaced_line);
+  res
+}
+
+fn main() {
+  let args: Vec<String> = env::args().collect();
+  if args.len() != 2 {
+    println!("Wrong number of arguments. Provide just a file name.");
+    process::exit(1);
+  }
+  let filename = &args[1];
+  println!("Using file {} as input.", filename);
+  let f = match File::open(filename) {
+    Ok(file) => file,
+    Err(e) => {
+      println!("Failed to open file {}. {:?}", filename, e);
+      process::exit(1);
+    }
+  };
+  let file = BufReader::new(&f);
+  let mut lines: Vec<String> = file.lines()
+    .map(|line| line.expect("Could not parse line."))
+    .collect();
+  &lines.sort();
+  assert_eq!(lines.len(), 1);
+  let line = &lines[0];
+
+  // exercise 1
+  println!("Solving 1...");
+  let result = react_polymer(&line);
+
+  // println!("1. Result: {}", result);
+  println!("1. Length: {}", result.len());
+
+  // exercise 2
+  println!("Solving 2...");
+  let mut best = line.len();
+  for ch in &ASCII_LOWER {
+    let result = react_polymer_without_char(&line, ch);
+    let len = result.len();
+    println!("Debug: ch: {}, len: {}", &ch, &len);
+    if len < best {
+      best = len;
+      println!("Debug: new best: {}", &len);
+    }
+  }
+  println!("2. Length: {}", best);
+}
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