2190. Most Frequent Number Following Key In an Array: AC

Author: tan-wei

src/solution/mod.rs

@@ -1655,3 +1655,4 @@ mod s2185_counting_words_with_a_given_prefix;
 mod s2186_minimum_number_of_steps_to_make_two_strings_anagram_ii;
 mod s2187_minimum_time_to_complete_trips;
 mod s2188_minimum_time_to_finish_the_race;
+mod s2190_most_frequent_number_following_key_in_an_array;

src/solution/s2190_most_frequent_number_following_key_in_an_array.rs

@@ -0,0 +1,87 @@
+/**
+ * [2190] Most Frequent Number Following Key In an Array
+ *
+ * You are given a 0-indexed integer array nums. You are also given an integer key, which is present in nums.
+ * For every unique integer target in nums, count the number of times target immediately follows an occurrence of key in nums. In other words, count the number of indices i such that:
+ *
+ * 	0 <= i <= nums.length - 2,
+ * 	nums[i] == key and,
+ * 	nums[i + 1] == target.
+ *
+ * Return the target with the maximum count. The test cases will be generated such that the target with maximum count is unique.
+ *  
+ * Example 1:
+ *
+ * Input: nums = [1,100,200,1,100], key = 1
+ * Output: 100
+ * Explanation: For target = 100, there are 2 occurrences at indices 1 and 4 which follow an occurrence of key.
+ * No other integers follow an occurrence of key, so we return 100.
+ *
+ * Example 2:
+ *
+ * Input: nums = [2,2,2,2,3], key = 2
+ * Output: 2
+ * Explanation: For target = 2, there are 3 occurrences at indices 1, 2, and 3 which follow an occurrence of key.
+ * For target = 3, there is only one occurrence at index 4 which follows an occurrence of key.
+ * target = 2 has the maximum number of occurrences following an occurrence of key, so we return 2.
+ *
+ *  
+ * Constraints:
+ *
+ * 	2 <= nums.length <= 1000
+ * 	1 <= nums[i] <= 1000
+ * 	The test cases will be generated such that the answer is unique.
+ *
+ */
+pub struct Solution {}
+
+// problem: https://leetcode.com/problems/most-frequent-number-following-key-in-an-array/
+// discuss: https://leetcode.com/problems/most-frequent-number-following-key-in-an-array/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+impl Solution {
+    pub fn most_frequent(nums: Vec<i32>, key: i32) -> i32 {
+        nums.windows(2)
+            .fold(
+                std::collections::HashMap::<_, u32>::with_capacity(nums.len()),
+                |mut map, win| {
+                    if win[0] == key {
+                        map.entry(win[1]).and_modify(|v| *v += 1).or_default();
+                    }
+                    map
+                },
+            )
+            .into_iter()
+            .max_by_key(|(_, v)| *v)
+            .unwrap()
+            .0
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_2190_example_1() {
+        let nums = vec![1, 100, 200, 1, 100];
+        let key = 1;
+
+        let result = 100;
+
+        assert_eq!(Solution::most_frequent(nums, key), result);
+    }
+
+    #[test]
+    fn test_2190_example_2() {
+        let nums = vec![2, 2, 2, 2, 3];
+        let key = 2;
+
+        let result = 2;
+
+        assert_eq!(Solution::most_frequent(nums, key), result);
+    }
+}