Add problem 2013: Detect Squares

src/lib.rs

@@ -1487,6 +1487,7 @@ pub mod problem_2007_find_original_array_from_doubled_array;
 pub mod problem_2008_maximum_earnings_from_taxi;
 pub mod problem_2011_final_value_of_variable_after_performing_operations;
 pub mod problem_2012_sum_of_beauty_in_the_array;
+pub mod problem_2013_detect_squares;
 pub mod problem_2016_maximum_difference_between_increasing_elements;
 pub mod problem_2017_grid_game;
 pub mod problem_2018_check_if_word_can_be_placed_in_crossword;

src/problem_2013_detect_squares/hash_map.rs

@@ -0,0 +1,85 @@
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+
+pub struct DetectSquares {
+    points: HashMap<u16, HashMap<u16, u16>>,
+}
+
+impl DetectSquares {
+    fn new() -> Self {
+        Self { points: HashMap::new() }
+    }
+
+    fn add(&mut self, point: Vec<i32>) {
+        let [x, y]: [_; 2] = point.try_into().ok().unwrap();
+        let x = x as u16;
+        let y = y as u16;
+
+        match self.points.entry(x) {
+            Entry::Occupied(entry) => match entry.into_mut().entry(y) {
+                Entry::Occupied(entry) => *entry.into_mut() += 1,
+                Entry::Vacant(entry) => {
+                    entry.insert(1);
+                }
+            },
+            Entry::Vacant(entry) => {
+                entry.insert(HashMap::from([(y, 1)]));
+            }
+        }
+    }
+
+    fn count(&self, point: Vec<i32>) -> i32 {
+        let [x_0, y_0]: [_; 2] = point.try_into().ok().unwrap();
+        let x_0 = x_0 as u16;
+        let y_0 = y_0 as u16;
+        let mut result = 0;
+
+        if let Some(column_0) = self.points.get(&x_0) {
+            for (&y_1, &count_0) in column_0 {
+                if y_0 == y_1 {
+                    continue;
+                }
+
+                let d = y_1.wrapping_sub(y_0);
+
+                for x_1 in [x_0.wrapping_sub(d), x_0.wrapping_add(d)] {
+                    if let Some(column_1) = self.points.get(&x_1) {
+                        if let Some(&count_1) = column_1.get(&y_0) {
+                            if let Some(&count_2) = column_1.get(&y_1) {
+                                result += u32::from(count_0) * u32::from(count_1) * u32::from(count_2);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+        result as _
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::DetectSquares for DetectSquares {
+    fn new() -> Self {
+        Self::new()
+    }
+
+    fn add(&mut self, point: Vec<i32>) {
+        self.add(point);
+    }
+
+    fn count(&self, point: Vec<i32>) -> i32 {
+        self.count(point)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::DetectSquares>();
+    }
+}