Add day 25

Author: LinAGKar

Day25_input.txt

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+15733400
+6408062

day25a/Cargo.toml

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+[package]
+name = "day25a"
+version = "0.1.0"
+authors = ["Linus Kardell <[email protected]>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day25a/src/main.rs

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+use std::io::Read;
+
+fn main() {
+    const MOD: u32 = 20201227;
+    const PUB_SUB: u32 = 7;
+
+    let mut input = String::new();
+    std::io::stdin().read_to_string(&mut input).unwrap();
+
+    let pub_keys: Vec<u32> = input.lines().map(|line| line.parse().unwrap()).collect();
+
+    let loop_size = (1..).try_fold(1, |acc, i| {
+        let val = acc * PUB_SUB % MOD;
+        if val == pub_keys[0] {
+            Err(i)
+        } else {
+            Ok(val)
+        }
+    }).err().unwrap();
+
+    println!("{}", (0..loop_size).fold(1, |acc, _| acc * pub_keys[1] as u64 % MOD as u64));
+}