From 9e1a52e931c6d14fb8aac98cb23094208d488e3c Mon Sep 17 00:00:00 2001
From: Johannes <jschaef@mail.uni-paderborn.de>
Date: Sun, 1 Dec 2019 10:00:24 +0100
Subject: [PATCH] day01 use successors

---
 src/tasks/day01.rs | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/src/tasks/day01.rs b/src/tasks/day01.rs
index b586cf9..82febad 100644
--- a/src/tasks/day01.rs
+++ b/src/tasks/day01.rs
@@ -22,19 +22,21 @@ fn task1(content: &String) {
 }
 
 fn task2(content: &String) {
-    fn while_fun(mass: i32) -> i32 {
-        let to_add = mass / 3 - 2;
-        if to_add < 1 {
-            0
-        } else {
-            to_add + while_fun(to_add)
-        }
-    };
-
     let fuel: i32 = content
         .lines()
         .map(|line| line.parse::<i32>().unwrap())
-        .map(while_fun)
+        .map(|mass| {
+            std::iter::successors(Some(mass), |m| {
+                let needed_fuel = m / 3 - 2;
+                if needed_fuel > 0 {
+                    Some(needed_fuel)
+                } else {
+                    None
+                }
+            })
+            .skip(1)
+            .sum::<i32>()
+        })
         .sum();
 
     println!("Task 2: {}", fuel);