Add day 5 part 2 solution

2017/day/5/src/main.rs

@@ -11,7 +11,10 @@ fn main() {
         .collect::<Vec<_>>();
 
     let steps = steps_to_exit(&offsets);
-    println!("{}", steps);
+    println!("Part 1: {}", steps);
+
+    let steps = steps_to_exit_part2(&offsets);
+    println!("Part 2: {}", steps);
 }
 
 fn steps_to_exit(jump_offsets: &[i32]) -> i32 {
@@ -37,8 +40,45 @@ fn steps_to_exit(jump_offsets: &[i32]) -> i32 {
     steps
 }
 
+fn steps_to_exit_part2(jump_offsets: &[i32]) -> i32 {
+    let mut offsets = jump_offsets.to_vec();
+    let mut pc = 0i32;
+    let mut steps = 0;
+
+    loop {
+        if let Some(offset) = offsets.get_mut(pc as usize) {
+            pc += *offset;
+            if *offset >= 3 {
+                *offset -= 1;
+            }
+            else {
+                *offset += 1;
+            }
+            steps += 1;
+        }
+        else {
+            break;
+        }
+
+        if pc < 0 {
+            break;
+        }
+    }
+
+    steps
+}
+
 #[test]
 fn test_example() {
     let jumps = vec![0, 3, 0, 1, -3];
     assert_eq!(steps_to_exit(&jumps), 5);
 }
+
+// Using this rule with the above example, the process now takes 10 steps, and the offset values
+// after finding the exit are left as 2 3 2 3 -1.
+#[test]
+fn test_example_part2() {
+    let jumps = vec![0, 3, 0, 1, -3];
+    assert_eq!(steps_to_exit_part2(&jumps), 10);
+}
+