day9 part1

day09/src/main.rs

@@ -0,0 +1,34 @@
+use std::fs;
+
+fn main() {
+    let input = fs::read_to_string("input.txt").unwrap();
+    let input: Vec<_> = input.split('\n')
+        .map(|line| {
+            line.split_whitespace()
+                .map(|num| num.parse::<i64>().unwrap())
+                .collect::<Vec<_>>()
+        }).collect();
+
+    let mut total = 0;
+
+    for line in input {
+        let mut line_enders: Vec<i64> = vec![*line.last().unwrap()];
+        let mut cur_line: Vec<i64> = line;
+        while !cur_line.iter().all(|x| *x == 0) {
+            let mut next_line: Vec<i64> = vec![];
+            for i in 1..cur_line.len() {
+                let diff = cur_line[i] - cur_line[i-1];
+                next_line.push(diff)
+            }
+            line_enders.push(*next_line.last().unwrap());
+            cur_line = next_line;
+        }
+
+        let mut sum = 0;
+        for i in (1..line_enders.len()).rev() {
+            sum = sum + line_enders[i - 1];
+        }
+        total += sum;
+    }
+    println!("{:?}", total)
+}