Day 6!

inputs/day6_test.txt

@@ -0,0 +1,15 @@
+abc
+
+a
+b
+c
+
+ab
+ac
+
+a
+a
+a
+a
+
+b

src/bin/customs_form.rs

@@ -0,0 +1,82 @@
+use advent2020::errors::TopLevelError;
+use std::collections::BTreeSet;
+use std::env;
+use std::fs;
+
+fn real_main() -> Result<(), TopLevelError> {
+    let mut customs_forms_any = Vec::new();
+    let mut customs_forms_all = Vec::new();
+
+    for argument in env::args().skip(1) {
+        let contents = fs::read_to_string(argument)?;
+        let mut current_form_any = BTreeSet::new();
+        let mut current_form_all = every_seat();
+
+        for line in contents.lines() {
+            if line.is_empty() {
+                customs_forms_any.push(current_form_any);
+                customs_forms_all.push(current_form_all);
+                current_form_any = BTreeSet::new();
+                current_form_all = every_seat();
+            } else {
+                let mut person_answers = BTreeSet::new();
+
+                for char in line.chars() {
+                    person_answers.insert(char);
+                }
+
+                current_form_any = current_form_any.union(&person_answers).cloned().collect();
+                current_form_all = current_form_all
+                    .intersection(&person_answers)
+                    .cloned()
+                    .collect();
+            }
+        }
+        customs_forms_any.push(current_form_any);
+        customs_forms_all.push(current_form_all);
+    }
+
+    let mut sum_all = 0;
+    let mut sum_any = 0;
+
+    for (form_any, form_all) in customs_forms_any.iter().zip(customs_forms_all.iter()) {
+        println!(
+            "Form: any |{}| / all |{}|",
+            display_form(form_any),
+            display_form(form_all)
+        );
+        sum_any += form_any.len();
+        sum_all += form_all.len();
+    }
+
+    println!("Checked boxes (any): {}", sum_any);
+    println!("Checked boxes (all): {}", sum_all);
+
+    Ok(())
+}
+
+fn display_form(x: &BTreeSet<char>) -> String {
+    let mut retval = String::new();
+
+    for char in x.iter() {
+        retval.push(*char);
+    }
+
+    retval
+}
+
+fn every_seat() -> BTreeSet<char> {
+    let mut result = BTreeSet::new();
+
+    for c in 'a'..='z' {
+        result.insert(c);
+    }
+
+    result
+}
+
+fn main() {
+    if let Err(e) = real_main() {
+        eprintln!("ERROR: {}", e);
+    }
+}