20250418 finished.

src/problem/mod.rs

@@ -605,3 +605,5 @@ mod p2179_count_good_triplets_in_an_array;
 mod p2537_count_the_number_of_good_subarrays;
 
 mod p2176_count_equal_and_divisible_pairs_in_an_array;
+
+mod p2364_count_number_of_bad_pairs;

src/problem/p2364_count_number_of_bad_pairs.rs

@@ -0,0 +1,41 @@
+/**
+ * [2364] Count Number of Bad Pairs
+ */
+pub struct Solution {}
+
+// submission codes start here
+use std::collections::HashMap;
+
+impl Solution {
+    pub fn count_bad_pairs(nums: Vec<i32>) -> i64 {
+        let n = nums.len() as i64;
+        let mut map = HashMap::new();
+
+        for (i, v) in nums.into_iter().enumerate() {
+            let delta = v - i as i32;
+            let mut entry = map.entry(delta).or_insert(0);
+            *entry += 1;
+        }
+
+        // 反过来计算好数对的数量
+        let good_pair_count = map
+            .values()
+            .filter_map(|&v| if v >= 2 { Some(v * (v - 1) / 2) } else { None })
+            .sum::<i64>();
+
+        n * (n - 1) / 2 - good_pair_count
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_2364() {
+        assert_eq!(5, Solution::count_bad_pairs(vec![4, 1, 3, 3]));
+        assert_eq!(0, Solution::count_bad_pairs(vec![1, 2, 3, 4, 5]));
+    }
+}