Pov exercise

.gitignore

@@ -6,6 +6,7 @@ tmp
 /bin/configlet
 exercises/*/*/Cargo.lock
 clippy.log
+.idea
 .vscode
 .prob-spec
 problem-specifications

config.json

@@ -1572,6 +1572,15 @@
           "lists",
           "unsafe"
         ]
+      },
+      {
+        "slug": "pov",
+        "name": "POV",
+        "uuid": "bf7b7309-3d34-4893-a584-f7742502e012",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 10,
+        "topics": []
       }
     ],
     "foregone": [

exercises/practice/pov/.docs/instructions.md

@@ -0,0 +1,41 @@
+# Instructions
+
+Reparent a tree on a selected node.
+
+A [tree][wiki-tree] is a special type of [graph][wiki-graph] where all nodes are connected but there are no cycles.
+That means, there is exactly one path to get from one node to another for any pair of nodes.
+
+This exercise is all about re-orientating a tree to see things from a different point of view.
+For example family trees are usually presented from the ancestor's perspective:
+
+```text
+    +------0------+
+    |      |      |
+  +-1-+  +-2-+  +-3-+
+  |   |  |   |  |   |
+  4   5  6   7  8   9
+```
+
+But there is no inherent direction in a tree.
+The same information can be presented from the perspective of any other node in the tree, by pulling it up to the root and dragging its relationships along with it.
+So the same tree from 6's perspective would look like:
+
+```text
+        6
+        |
+  +-----2-----+
+  |           |
+  7     +-----0-----+
+        |           |
+      +-1-+       +-3-+
+      |   |       |   |
+      4   5       8   9
+```
+
+This lets us more simply describe the paths between two nodes.
+So for example the path from 6-9 (which in the first tree goes up to the root and then down to a different leaf node) can be seen to follow the path 6-2-0-3-9.
+
+This exercise involves taking an input tree and re-orientating it from the point of view of one of the nodes.
+
+[wiki-graph]: https://en.wikipedia.org/wiki/Tree_(graph_theory)
+[wiki-tree]: https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)

exercises/practice/pov/.gitignore

@@ -0,0 +1,2 @@
+/target
+Cargo.lock

exercises/practice/pov/.meta/config.json

@@ -0,0 +1,20 @@
+{
+  "authors": [
+    "devcyjung"
+  ],
+  "files": {
+    "solution": [
+      "src/lib.rs",
+      "Cargo.toml"
+    ],
+    "test": [
+      "tests/pov.rs"
+    ],
+    "example": [
+      ".meta/example.rs"
+    ]
+  },
+  "blurb": "Reparent a graph on a selected node.",
+  "source": "Adaptation of exercise from 4clojure",
+  "source_url": "https://github.com/oxalorg/4ever-clojure"
+}

exercises/practice/pov/.meta/example.rs

@@ -0,0 +1,96 @@
+use std::fmt::Debug;
+use std::ops::{Deref, DerefMut};
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct Tree<T: Clone + Debug + PartialEq> {
+    label: T,
+    children: Vec<Box<Tree<T>>>,
+}
+
+impl<T: Clone + Debug + PartialEq> Tree<T> {
+    #[must_use]
+    pub fn new(label: T) -> Self {
+        Self {
+            label,
+            children: Default::default(),
+        }
+    }
+
+    #[must_use]
+    pub fn with_children(label: T, children: Vec<Self>) -> Self {
+        Self {
+            label,
+            children: children.into_iter().map(Box::new).collect(),
+        }
+    }
+
+    #[must_use]
+    pub fn get_label(&self) -> T {
+        self.label.clone()
+    }
+
+    #[must_use]
+    pub fn get_children(&self) -> Vec<&Self> {
+        self.children.iter().map(Box::deref).collect()
+    }
+
+    #[must_use]
+    pub fn pov_from(&self, from: &T) -> Option<Self> {
+        // list of (child, parent, child's index in parent.children)
+        let mut lookup = vec![(self, None, None)];
+        let mut stack = vec![self];
+        while let Some(parent) = stack.pop() {
+            if &parent.label == from {
+                return self.reparent(parent, lookup.as_slice()).into();
+            }
+            lookup.extend(
+                parent
+                    .children
+                    .iter()
+                    .map(Box::deref)
+                    .enumerate()
+                    .map(|(i, child)| (child, Some(parent), Some(i))),
+            );
+            stack.extend(parent.children.iter().map(Box::deref));
+        }
+        None
+    }
+
+    // lookup is list of (child, parent, child's index in parent.children)
+    #[must_use]
+    fn reparent(&self, parent: &Self, lookup: &[(&Self, Option<&Self>, Option<usize>)]) -> Self {
+        let mut new_root = parent.clone();
+        let mut current = parent;
+        let mut clone_mut = &mut new_root;
+        let find_parent = |child| lookup.iter().find(|(c, _p, _i)| *c == child);
+        while let Some(&(_, Some(parent), Some(index))) = find_parent(current) {
+            let mut parent_clone = parent.clone();
+            parent_clone.children.swap_remove(index);
+            clone_mut.children.push(Box::new(parent_clone));
+            current = parent;
+            let new_box = clone_mut
+                .children
+                .last_mut()
+                .expect("We just inserted node, this is not empty");
+            clone_mut = new_box.deref_mut();
+        }
+        new_root
+    }
+
+    #[must_use]
+    pub fn path_to(&self, from: &T, to: &T) -> Option<Vec<T>> {
+        if from != &self.label {
+            return self.pov_from(from).and_then(|pov| pov.path_to(from, to));
+        }
+        if to == &self.label {
+            return Some(vec![self.label.clone()]);
+        }
+        for child in self.children.iter() {
+            if let Some(mut path) = child.path_to(&child.label, to) {
+                path.insert(0, self.label.clone());
+                return Some(path);
+            }
+        }
+        None
+    }
+}

exercises/practice/pov/.meta/test_template.tera

@@ -0,0 +1,68 @@
+{%- macro render_tree(tree) -%}
+{%- if tree.children -%}
+    Tree::with_children(
+        "{{ tree.label }}".to_string(),
+        vec![
+            {%- for child in tree.children -%}
+                {{ self::render_tree(tree=child) }},
+            {%- endfor -%}
+        ],
+    )
+{%- else -%}
+    Tree::new("{{ tree.label }}".to_string())
+{%- endif -%}
+{%- endmacro -%}
+
+{%- macro render_vec(values) -%}
+vec![
+    {%- for value in values -%}
+        "{{ value }}".to_string(),
+    {%- endfor -%}
+]
+{%- endmacro -%}
+
+{% for test_group in cases %}
+/// {{ test_group.description }}
+mod {{ test_group.cases[0].property | make_ident }} {
+    use pov::*;
+    use pretty_assertions::assert_eq;
+
+{% for test in test_group.cases %}
+#[test]
+#[ignore]
+fn {{ test.description | make_ident }}() {
+    let input = {{ self::render_tree(tree=test.input.tree) }};
+    let from = "{{ test.input.from }}".to_string();
+    {%- if test.property == "fromPov" -%}
+        let result = input.pov_from(&from);
+        {%- if not test.expected -%}
+            let expected: Option<Tree<String>> = None;
+        {%- else -%}
+            let expected = Some({{ self::render_tree(tree=test.expected) }});
+        {%- endif -%}
+        assert_eq!(result.map(|t| crate::test_util::tree_to_sorted(&t)), expected.map(|t| crate::test_util::tree_to_sorted(&t)));
+    {%- elif test.property == "pathTo" -%}
+        let to = "{{ test.input.to }}".to_string();
+        let result = input.path_to(&from, &to);
+        {%- if not test.expected -%}
+            let expected: Option<Vec<String>> = None;
+        {%- else -%}
+            let expected = Some({{ self::render_vec(values=test.expected) }});
+        {%- endif -%}
+        assert_eq!(result, expected);
+    {%- else -%}
+        Invalid property: {{ test.property }}
+    {%- endif -%}
+}
+{% endfor %}
+}
+{% endfor %}
+
+mod test_util {
+    use pov::*;
+    pub fn tree_to_sorted<T: Ord + Clone + std::fmt::Debug>(tree: &Tree<T>) -> Tree<T> {
+        let mut children = tree.get_children();
+        children.sort_unstable_by_key(|child| child.get_label());
+        Tree::with_children(tree.get_label(), children.iter().map(|c| tree_to_sorted(c)).collect())
+    }
+}

exercises/practice/pov/.meta/tests.toml

@@ -0,0 +1,55 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[1b3cd134-49ad-4a7d-8376-7087b7e70792]
+description = "Reroot a tree so that its root is the specified node. -> Results in the same tree if the input tree is a singleton"
+
+[0778c745-0636-40de-9edd-25a8f40426f6]
+description = "Reroot a tree so that its root is the specified node. -> Can reroot a tree with a parent and one sibling"
+
+[fdfdef0a-4472-4248-8bcf-19cf33f9c06e]
+description = "Reroot a tree so that its root is the specified node. -> Can reroot a tree with a parent and many siblings"
+
+[cbcf52db-8667-43d8-a766-5d80cb41b4bb]
+description = "Reroot a tree so that its root is the specified node. -> Can reroot a tree with new root deeply nested in tree"
+
+[e27fa4fa-648d-44cd-90af-d64a13d95e06]
+description = "Reroot a tree so that its root is the specified node. -> Moves children of the new root to same level as former parent"
+
+[09236c7f-7c83-42cc-87a1-25afa60454a3]
+description = "Reroot a tree so that its root is the specified node. -> Can reroot a complex tree with cousins"
+
+[f41d5eeb-8973-448f-a3b0-cc1e019a4193]
+description = "Reroot a tree so that its root is the specified node. -> Errors if target does not exist in a singleton tree"
+
+[9dc0a8b3-df02-4267-9a41-693b6aff75e7]
+description = "Reroot a tree so that its root is the specified node. -> Errors if target does not exist in a large tree"
+
+[02d1f1d9-428d-4395-b026-2db35ffa8f0a]
+description = "Given two nodes, find the path between them -> Can find path to parent"
+
+[d0002674-fcfb-4cdc-9efa-bfc54e3c31b5]
+description = "Given two nodes, find the path between them -> Can find path to sibling"
+
+[c9877cd1-0a69-40d4-b362-725763a5c38f]
+description = "Given two nodes, find the path between them -> Can find path to cousin"
+
+[9fb17a82-2c14-4261-baa3-2f3f234ffa03]
+description = "Given two nodes, find the path between them -> Can find path not involving root"
+
+[5124ed49-7845-46ad-bc32-97d5ac7451b2]
+description = "Given two nodes, find the path between them -> Can find path from nodes other than x"
+
+[f52a183c-25cc-4c87-9fc9-0e7f81a5725c]
+description = "Given two nodes, find the path between them -> Errors if destination does not exist"
+
+[f4fe18b9-b4a2-4bd5-a694-e179155c2149]
+description = "Given two nodes, find the path between them -> Errors if source does not exist"

exercises/practice/pov/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "pov"
+version = "0.1.0"
+edition = "2024"
+
+# Not all libraries from crates.io are available in Exercism's test runner.
+# The full list of available libraries is here:
+# https://github.com/exercism/rust-test-runner/blob/main/local-registry/Cargo.toml
+[dependencies]
+
+[dev-dependencies]
+pretty_assertions = "1.4.1"

exercises/practice/pov/src/lib.rs

@@ -0,0 +1,34 @@
+use std::fmt::Debug;
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct Tree<T: Clone + Debug + PartialEq> {
+    _remove_this: std::marker::PhantomData<T>,
+}
+
+impl<T: Clone + Debug + PartialEq> Tree<T> {
+    pub fn new(label: T) -> Self {
+        todo!("Implement a function that creates a new Tree with given {label:?}");
+    }
+
+    pub fn with_children(label: T, children: Vec<Self>) -> Self {
+        todo!("Implement a function that creates a new Tree with given {label:?} and {children:?}");
+    }
+
+    pub fn get_label(&self) -> T {
+        todo!("Implement getter for label.");
+    }
+
+    pub fn get_children(&self) -> Vec<&Self> {
+        todo!("Implement getter for children.");
+    }
+
+    pub fn pov_from(&self, from: &T) -> Option<Self> {
+        todo!("Implement a function that reparents Tree with {from:?} as root.");
+    }
+
+    pub fn path_to(&self, from: &T, to: &T) -> Option<Vec<T>> {
+        todo!(
+            "Implement a function that returns the list of labels in the shortest path from {from:?} to {to:?}"
+        );
+    }
+}