2364. Count Number of Bad Pairs: AC

Author: tan-wei

src/solution/mod.rs

@@ -1790,3 +1790,4 @@ mod s2358_maximum_number_of_groups_entering_a_competition;
 mod s2359_find_closest_node_to_given_two_nodes;
 mod s2360_longest_cycle_in_a_graph;
 mod s2363_merge_similar_items;
+mod s2364_count_number_of_bad_pairs;

src/solution/s2364_count_number_of_bad_pairs.rs

@@ -0,0 +1,76 @@
+/**
+ * [2364] Count Number of Bad Pairs
+ *
+ * You are given a 0-indexed integer array nums. A pair of indices (i, j) is a bad pair if i < j and j - i != nums[j] - nums[i].
+ * Return the total number of bad pairs in nums.
+ *  
+ * Example 1:
+ *
+ * Input: nums = [4,1,3,3]
+ * Output: 5
+ * Explanation: The pair (0, 1) is a bad pair since 1 - 0 != 1 - 4.
+ * The pair (0, 2) is a bad pair since 2 - 0 != 3 - 4, 2 != -1.
+ * The pair (0, 3) is a bad pair since 3 - 0 != 3 - 4, 3 != -1.
+ * The pair (1, 2) is a bad pair since 2 - 1 != 3 - 1, 1 != 2.
+ * The pair (2, 3) is a bad pair since 3 - 2 != 3 - 3, 1 != 0.
+ * There are a total of 5 bad pairs, so we return 5.
+ *
+ * Example 2:
+ *
+ * Input: nums = [1,2,3,4,5]
+ * Output: 0
+ * Explanation: There are no bad pairs.
+ *
+ *  
+ * Constraints:
+ *
+ * 	1 <= nums.length <= 10^5
+ * 	1 <= nums[i] <= 10^9
+ *
+ */
+pub struct Solution {}
+
+// problem: https://leetcode.com/problems/count-number-of-bad-pairs/
+// discuss: https://leetcode.com/problems/count-number-of-bad-pairs/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+impl Solution {
+    pub fn count_bad_pairs(nums: Vec<i32>) -> i64 {
+        nums.into_iter()
+            .enumerate()
+            .map(|(i, num)| (i, num - i as i32))
+            .scan(std::collections::HashMap::new(), |map, (i, num)| {
+                let same_count = map.entry(num).or_insert(0);
+                let diff_count = i as i32 - *same_count;
+                *same_count += 1;
+                Some(diff_count as i64)
+            })
+            .sum()
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_2364_example_1() {
+        let nums = vec![4, 1, 3, 3];
+
+        let result = 5;
+
+        assert_eq!(Solution::count_bad_pairs(nums), result);
+    }
+
+    #[test]
+    fn test_2364_example_2() {
+        let nums = vec![1, 2, 3, 4, 5];
+
+        let result = 0;
+
+        assert_eq!(Solution::count_bad_pairs(nums), result);
+    }
+}