day15

day15/Cargo.toml

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+[package]
+name = "day15"
+version = "0.1.0"
+authors = ["henine <why@no.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day15/src/main.rs

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+// use std::collections::HashMap;
+
+fn main() {
+    // let input = vec![0, 3, 6];
+    let input:Vec<i32> = vec![20, 9, 11, 0, 1, 2];
+
+    // let mut memory: HashMap<i32, usize> = HashMap::new();
+    let mut memory: Vec<Option<i32>> = Vec::with_capacity(30_000_000);
+    for _i in 0..30_000_000 {
+        memory.push(None)
+    }
+    let mut last = input[0];
+
+    for turn in 1..30_000_000 {
+        let new_last = if turn <= input.len() - 1 {
+            input[turn]
+        } else {
+            match memory.get(last as usize) {
+                Some(Some(last_turn)) => {
+                    (turn as i32 - last_turn) as i32
+                }
+                Some(None) => {
+                    0
+                }
+                _ => panic!()
+            }
+        };
+
+        // memory.insert(last, turn);
+        memory[last as usize] = Some(turn as i32);
+
+        last = new_last;
+
+        if turn % 1000000 == 0 {
+            println!("{}/30000000 \t- {:.2}%", turn, turn as f32 / 30000000f32 * 100f32)
+        }
+
+        // println!("Turn: {}\t\t Next Number: {}", turn, last);
+        // println!("{:?}", memory)
+    }
+    println!("Number: {}", last);
+}