From 96d6b41260104563ab505c9156044034da01ec48 Mon Sep 17 00:00:00 2001
From: EFanZh <efanzh@gmail.com>
Date: Mon, 16 Dec 2024 22:12:17 +0800
Subject: [PATCH] Add problem 2364: Count Number of Bad Pairs

---
 src/lib.rs                                    |  1 +
 .../iterative.rs                              | 51 +++++++++++++++++++
 .../mod.rs                                    | 18 +++++++
 3 files changed, 70 insertions(+)
 create mode 100644 src/problem_2364_count_number_of_bad_pairs/iterative.rs
 create mode 100644 src/problem_2364_count_number_of_bad_pairs/mod.rs

diff --git a/src/lib.rs b/src/lib.rs
index e90c8219..1d3768b8 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1754,6 +1754,7 @@ pub mod problem_2357_make_array_zero_by_subtracting_equal_amounts;
 pub mod problem_2358_maximum_number_of_groups_entering_a_competition;
 pub mod problem_2360_longest_cycle_in_a_graph;
 pub mod problem_2363_merge_similar_items;
+pub mod problem_2364_count_number_of_bad_pairs;
 
 #[cfg(test)]
 mod test_utilities;
diff --git a/src/problem_2364_count_number_of_bad_pairs/iterative.rs b/src/problem_2364_count_number_of_bad_pairs/iterative.rs
new file mode 100644
index 00000000..7344353a
--- /dev/null
+++ b/src/problem_2364_count_number_of_bad_pairs/iterative.rs
@@ -0,0 +1,51 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+
+impl Solution {
+    pub fn count_bad_pairs(nums: Vec<i32>) -> i64 {
+        let n = nums.len();
+        let mut counts = HashMap::new();
+        let mut good_pairs = 0;
+
+        (0..).zip(nums).for_each(|(i, num)| {
+            let key = num - i;
+
+            match counts.entry(key) {
+                Entry::Occupied(occupied_entry) => {
+                    let count = occupied_entry.into_mut();
+
+                    good_pairs += *count;
+
+                    *count += 1;
+                }
+                Entry::Vacant(vacant_entry) => {
+                    vacant_entry.insert(1);
+                }
+            }
+        });
+
+        let n = n as u64;
+
+        (n * (n - 1) / 2 - good_pairs) as _
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn count_bad_pairs(nums: Vec<i32>) -> i64 {
+        Self::count_bad_pairs(nums)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}
diff --git a/src/problem_2364_count_number_of_bad_pairs/mod.rs b/src/problem_2364_count_number_of_bad_pairs/mod.rs
new file mode 100644
index 00000000..d52c8620
--- /dev/null
+++ b/src/problem_2364_count_number_of_bad_pairs/mod.rs
@@ -0,0 +1,18 @@
+pub mod iterative;
+
+pub trait Solution {
+    fn count_bad_pairs(nums: Vec<i32>) -> i64;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [(&[4, 1, 3, 3] as &[_], 5), (&[1, 2, 3, 4, 5], 0)];
+
+        for (nums, expected) in test_cases {
+            assert_eq!(S::count_bad_pairs(nums.to_vec()), expected);
+        }
+    }
+}