Add problem 1365: How Many Numbers Are Smaller Than the Current Number

src/lib.rs

@@ -546,6 +546,7 @@ pub mod problem_1338_reduce_array_size_to_the_half;
 pub mod problem_1344_angle_between_hands_of_a_clock;
 pub mod problem_1346_check_if_n_and_its_double_exist;
 pub mod problem_1357_apply_discount_every_n_orders;
+pub mod problem_1365_how_many_numbers_are_smaller_than_the_current_number;
 pub mod problem_1375_number_of_times_binary_string_is_prefix_aligned;
 pub mod problem_1381_design_a_stack_with_increment_operation;
 pub mod problem_1387_sort_integers_by_the_power_value;

src/problem_1365_how_many_numbers_are_smaller_than_the_current_number/heap.rs

@@ -0,0 +1,40 @@
+pub struct Solution;
+
+use std::{
+    cmp::Reverse,
+    collections::{BinaryHeap, HashMap},
+};
+
+impl Solution {
+    pub fn smaller_numbers_than_current(nums: Vec<i32>) -> Vec<i32> {
+        let mut result = vec![0; nums.len()];
+        let mut map = HashMap::with_capacity(nums.len());
+        let mut heap: BinaryHeap<Reverse<_>> =
+            nums.into_iter().zip(0usize..).map(Reverse).collect();
+
+        let mut count = 0;
+        while let Some(Reverse((val, idx))) = heap.pop() {
+            if let Some(x) = map.insert(val, idx) {
+                result[idx] = result[x];
+            } else {
+                result[idx] = count;
+            }
+            count += 1;
+        }
+        result
+    }
+}
+
+impl super::Solution for Solution {
+    fn smaller_numbers_than_current(nums: Vec<i32>) -> Vec<i32> {
+        Self::smaller_numbers_than_current(nums)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_1365_how_many_numbers_are_smaller_than_the_current_number/mod.rs

@@ -0,0 +1,22 @@
+pub mod heap;
+
+pub trait Solution {
+    fn smaller_numbers_than_current(nums: Vec<i32>) -> Vec<i32>;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [
+            (&[8, 1, 2, 2, 3] as &[_], &[4, 0, 1, 1, 3] as &[_]),
+            (&[6, 5, 4, 8], &[2, 1, 0, 3]),
+            (&[7, 7, 7, 7], &[0, 0, 0, 0]),
+        ];
+
+        for (nums, expected) in test_cases {
+            assert_eq!(S::smaller_numbers_than_current(nums.to_vec()), expected);
+        }
+    }
+}