Challenge 73 Task 2 only, 2 alternative implementations

3 files changed, 81 insertions, 0 deletions

diff --git a/challenge-073/xkr47/rust/Cargo.toml b/challenge-073/xkr47/rust/Cargo.toml
new file mode 100644
index 0000000000..59facb0ade
--- /dev/null
+++ b/challenge-073/xkr47/rust/Cargo.toml
@@ -0,0 +1,16 @@
+[package]
+name = "pwd-073"
+version = "0.1.0"
+authors = ["Jonas Berlin <xkr47@outerspace.dyndns.org>"]
+edition = "2018"
+
+[dependencies]
+num-traits = "0.2"
+
+[[bin]]
+name = "ch-2"
+path = "ch-2.rs"
+
+[[bin]]
+name = "ch-2-2"
+path = "ch-2-2.rs"
diff --git a/challenge-073/xkr47/rust/ch-2-2.rs b/challenge-073/xkr47/rust/ch-2-2.rs
new file mode 100644
index 0000000000..87aefc5875
--- /dev/null
+++ b/challenge-073/xkr47/rust/ch-2-2.rs
@@ -0,0 +1,47 @@
+use std::ops::Deref;
+use num_traits::Bounded;
+
+// Alternate impl as an iterator
+
+fn main() {
+    let a = vec![7, 8, 3, 12, 10];
+    let o: Vec<i32> = doit(&a);
+    assert_eq!(o, vec![0, 7, 0, 3, 3]);
+
+    let a = vec![4, 6, 5];
+    let o: Vec<i32> = doit(&a);
+    assert_eq!(o, vec![0, 4, 4]);
+}
+
+fn doit(a: &Vec<i32>) -> Vec<i32> {
+    MinLeft::new(a.iter()).collect()
+}
+
+struct MinLeft<I, T: Bounded + Copy + Ord + Default> {
+    a: I,
+    min: T,
+}
+
+impl<I, T: Bounded + Copy + Ord + Default> MinLeft<I, T> {
+    fn new(a: I) -> MinLeft<I, T> {
+        MinLeft {
+            a,
+            min: T::max_value(),
+        }
+    }
+}
+
+impl<'a, T: Bounded + Copy + Ord + Default, P: Deref<Target=T>, I: Iterator<Item=P>> Iterator for MinLeft<I, T> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.a.next() {
+            Some(next) => {
+                let result = if self.min < *next { self.min } else { Default::default() };
+                self.min = self.min.min(*next);
+                Some(result)
+            },
+            None => None
+        }
+    }
+}
diff --git a/challenge-073/xkr47/rust/ch-2.rs b/challenge-073/xkr47/rust/ch-2.rs
new file mode 100644
index 0000000000..3cec5f12f5
--- /dev/null
+++ b/challenge-073/xkr47/rust/ch-2.rs
@@ -0,0 +1,18 @@
+fn main() {
+    let a = vec![7, 8, 3, 12, 10];
+    let o: Vec<i32> = doit(&a);
+    assert_eq!(o, vec![0, 7, 0, 3, 3]);
+
+    let a = vec![4, 6, 5];
+    let o: Vec<i32> = doit(&a);
+    assert_eq!(o, vec![0, 4, 4]);
+}
+
+fn doit(a: &Vec<i32>) -> Vec<i32> {
+    let mut min = i32::max_value();
+    a.iter().map(|next| {
+        let result = if min < *next { min } else { 0 };
+        min = min.min(*next);
+        result
+    }).collect()
+}