init

.gitignore

@@ -0,0 +1 @@
+/target

Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "peak-and-valley"
+version = "0.1.0"

Cargo.toml

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+[package]
+name = "peak-and-valley"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

src/main.rs

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+#[derive(PartialEq, Debug)]
+enum Order {
+    Up,
+    Down,
+    Stable,
+    Uninit,
+}
+
+fn find_peaks_and_valleys(values: &[isize]) -> Vec<usize> {
+    let mut peaks_and_valleys = vec![];
+    let mut order = Order::Uninit;
+    for i in 1..values.len() {
+        let previous = values[i - 1];
+        let current = values[i];
+
+        let new_order = match current - previous {
+            0 => Order::Stable,
+            x if x > 0 => Order::Up,
+            x if x < 0 => Order::Down,
+            _ => unreachable!(),
+        };
+
+        println!(
+            "Compared {previous} ({}) and {current} ({}). Current order is {order:?}, new order is {new_order:?}",
+            i - 1,
+            i
+        );
+
+        if order != new_order && order != Order::Uninit {
+            peaks_and_valleys.push(i);
+            println!("Order changed, pushing {}", i)
+        }
+        order = new_order;
+    }
+
+    peaks_and_valleys
+}
+
+fn main() {
+    println!("Hello, world!");
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    pub fn test() {
+        assert_eq!(
+            find_peaks_and_valleys(&[1, 2, 1, 3, 4, 5, 4, 5, 2, 1, 2, 3]),
+            vec![1, 2, 5, 9]
+        );
+    }
+
+    #[test]
+    pub fn test_flat() {
+        assert_eq!(find_peaks_and_valleys(&[1, 1, 1, 1]), vec![]);
+    }
+
+    #[test]
+    pub fn test_up_and_down() {
+        assert_eq!(
+            find_peaks_and_valleys(&[1, 0, 1, 0, 1, 0]),
+            vec![1, 2, 3, 4, 5]
+        );
+    }
+
+    #[test]
+    pub fn test_negative() {
+        assert_eq!(
+            find_peaks_and_valleys(&[-5, -10, -7, -15, -12]),
+            vec![1, 2, 3]
+        );
+    }
+}