1 files changed, 57 insertions, 0 deletions
diff --git a/2023/day09.rs b/2023/day09.rs
new file mode 100644
index 0000000..68037d5
--- /dev/null
+++ b/2023/day09.rs
@@ -0,0 +1,57 @@
+use std::fs::File;
+use std::io::Read;
+
+fn diff(arr: &Vec<i64>) -> Vec<i64> {
+    arr.iter()
+        .zip(arr.iter().skip(1))
+        .map(|(x, y)| y - x)
+        .collect()
+}
+
+fn main() {
+    // let filename = "in/day09.ref";
+    let filename = "in/day09.pzl";
+
+    let mut f = File::open(filename).expect("cannot open file");
+    let mut content = String::new();
+    f.read_to_string(&mut content).expect("cannot read file");
+    let lines = content.trim_end().split('\n');
+    // println!("{:?}", lines);
+
+    let mut inp: Vec<Vec<i64>> = Vec::new();
+    for line in lines {
+        let l: Vec<i64> = line.split(' ').map(|x| x.parse().unwrap()).collect();
+        inp.push(l);
+    }
+
+    let mut res1 = 0;
+    let mut res2 = 0;
+
+    for nums in inp.iter() {
+        let mut desc: Vec<Vec<i64>> = Vec::new();
+        desc.push(nums.clone());
+        let mut d = diff(&nums);
+        desc.push(d.clone());
+        while d.iter().filter(|x| **x != 0).collect::<Vec<_>>().len() != 0 {
+            d = diff(&d);
+            desc.push(d.clone());
+        }
+
+        let mut a: i64 = *desc[desc.len() - 2].last().unwrap();
+        for i in 0..desc.len() - 2 {
+            a = *desc[desc.len() - 3 - i].last().unwrap() + a;
+        }
+        res1 += a;
+
+        let mut b: i64 = desc[desc.len() - 2][0];
+        for i in 0..desc.len() - 2 {
+            b = desc[desc.len() - 3 - i][0] - b;
+        }
+        res2 += b;
+    }
+
+    println!("res1: {}", res1);
+    println!("res2: {}", res2);
+    assert_eq!(res1, 1938800261);
+    assert_eq!(res2, 1112);
+}