day 7 solution

2018/day7/Cargo.lock

@@ -0,0 +1,4 @@
+[[package]]
+name = "day7"
+version = "0.1.0"
+

2018/day7/src/main.rs

@@ -1,3 +1,104 @@
-fn main() {
-    println!("Hello, world!");
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+use std::iter::Iterator;
+use std::collections::{BTreeMap, HashMap};
+
+type Day7Map = BTreeMap<char, Vec<char>>;
+
+fn print_map(steps: &Day7Map) {
+    for (key, value) in steps {
+        print!("{}: ", key);
+        for val in value.iter() {
+            print!("{} ", val);
+        }
+        println!("");
+    }
+}
+
+fn calc_order(steps: &mut Day7Map) -> String {
+    let mut first_available = '_';
+    for (key, values) in steps.iter_mut() {
+        if values.is_empty() {
+            values.push('_');
+            first_available = *key;
+            break;
+        }
+    };
+
+    let mut final_result = String::from("");
+    if first_available == '_' {
+        final_result
+    } else {
+        for (_key, values) in steps.iter_mut() {
+            values.retain(|&x| x != first_available);
+        }
+        final_result.push(first_available);
+        final_result.push_str(calc_order(steps).as_str());
+        final_result
+    }
+}
+
+fn calc_time(steps: &mut Day7Map, time_elapsed: i64, workers: &mut HashMap<char, i64>) -> i64 {
+    let mut available: Vec<char> = Vec::new();
+
+    // decrement workers
+    for (_key, time_remaining) in workers.iter_mut() {
+        *time_remaining -= 1;
+    }
+
+    // remove finished workers
+    workers.retain(|&k, &mut count| {
+        if count == 0 {
+            for (_key, values) in steps.iter_mut() {
+                values.retain(|&x| x != k);
+            }
+            false
+        } else {
+            true
+        }
+    });
+
+    let mut needed_workers = 5 - workers.len();
+    let mut needs_work = false;
+    for (key, values) in steps.iter_mut() {
+        if values.is_empty() {
+            needs_work = true;
+            if needed_workers > 0 {
+                values.push('_');
+                available.push(*key);
+                needed_workers -= 1;
+                if needed_workers == 0 {
+                    break;
+                }
+            }
+        }
+    }
+
+    // return final sum of time
+    if !needs_work && workers.is_empty() {
+        return time_elapsed;
+    }
+
+    for new_step in available.iter() {
+        // add new work
+        workers.entry(*new_step).or_insert(*new_step as i64 - 4);
+    }
+    calc_time(steps, time_elapsed + 1, workers)
+}
+
+fn main() {
+    let mut steps: Day7Map = BTreeMap::new();
+    for line in BufReader::new(File::open("input").unwrap()).lines() {
+        let line_str = line.unwrap();
+        let mut chars = line_str.chars();
+        let prereq = chars.nth(5).unwrap();
+        let target = chars.nth(30).unwrap();
+        steps.entry(target).and_modify(|e| e.push(prereq)).or_insert(vec![prereq]);
+        steps.entry(prereq).or_insert(vec![]);
+    };
+    print_map(&steps);
+    let order = calc_order(&mut steps.clone());
+    println!("final order: {}", order);
+    let time = calc_time(&mut steps.clone(), 0, &mut HashMap::<char, i64>::new());
+    println!("time required for 5 workers: {}", time);
 }