LC 2501. Longest Square Streak in an Array (Rust)

Author: raul-sauco

README.md

@@ -719,6 +719,7 @@ to the solution in this repository.
 | [2486. Append Characters to String to Make Subsequence][lc2486]                               | 🟠 Medium  | [![rust](res/rs.png)][lc2486rs]                                                                       |
 | [2491. Divide Players Into Teams of Equal Skill][lc2491]                                      | 🟠 Medium  | [![rust](res/rs.png)][lc2491rs]                                                                       |
 | [2492. Minimum Score of a Path Between Two Cities][lc2492]                                    | 🟠 Medium  | [![python](res/py.png)][lc2492py] [![rust](res/rs.png)][lc2492rs]                                     |
+| [2501. Longest Square Streak in an Array][lc2501]                                             | 🟠 Medium  | [![rust](res/rs.png)][lc2501rs]                                                                       |
 | [2530. Maximal Score After Applying K Operations][lc2530]                                     | 🟠 Medium  | [![rust](res/rs.png)][lc2530rs]                                                                       |
 | [2540. Minimum Common Value][lc2540]                                                          | 🟢 Easy    | [![rust](res/rs.png)][lc2540rs]                                                                       |
 | [2542. Maximum Subsequence Score][lc2542]                                                     | 🟠 Medium  | [![rust](res/rs.png)][lc2542rs]                                                                       |
@@ -2362,6 +2363,8 @@ to the solution in this repository.
 [lc2492]: https://leetcode.com/problems/minimum-score-of-a-path-between-two-cities/
 [lc2492py]: leetcode/minimum-score-of-a-path-between-two-cities.py
 [lc2492rs]: leetcode/minimum-score-of-a-path-between-two-cities.rs
+[lc2501]: https://leetcode.com/problems/longest-square-streak-in-an-array/
+[lc2501rs]: leetcode/longest-square-streak-in-an-array.rs
 [lc2530]: https://leetcode.com/problems/maximal-score-after-applying-k-operations/
 [lc2530rs]: leetcode/maximal-score-after-applying-k-operations.rs
 [lc2540]: https://leetcode.com/problems/minimum-common-value/

leetcode/longest-square-streak-in-an-array.rs

@@ -0,0 +1,73 @@
+// 2501. Longest Square Streak in an Array
+// 🟠 Medium
+//
+// https://leetcode.com/problems/longest-square-streak-in-an-array/
+//
+// Tags: Array - Hash Table - Binary Search - Dynamic Programming - Sorting
+
+use std::collections::HashMap;
+
+struct Solution;
+impl Solution {
+    /// One way to do it is to sort the input vector, then visit each number, check if we can
+    /// append it to any of the existing sequences and either extend that sequence or create a new
+    /// one. We determine if we can append to existing sequences using a hashmap with the next
+    /// square that would go into the sequence as the key and the length that the sequence would
+    /// have, once we append that next sequence, as the value.
+    ///
+    /// Time complexity: O(nlog(n)) - We sort the input vector, after that O(n)
+    /// Space complexity: O(n) - The hashmap grows to size n.
+    ///
+    /// Runtime 28 ms Beats 100%
+    /// Memory 5.17 MB Beats 100%
+    pub fn longest_square_streak(mut nums: Vec<i32>) -> i32 {
+        nums.sort_unstable();
+        // A hashmap of the next squares with the sequence length.
+        let mut next_squares = HashMap::new();
+        let mut res = -1;
+        for num in nums {
+            // Skip duplicates.
+            if next_squares.contains_key(&(num * num)) {
+                continue;
+            }
+            // Can I append to an existing sequence?
+            if let Some(&counter) = next_squares.get(&num) {
+                res = res.max(counter);
+                next_squares.insert(num * num, counter + 1);
+            } else {
+                next_squares.insert(num * num, 2);
+            }
+        }
+        res
+    }
+}
+
+// Tests.
+fn main() {
+    let tests = [(vec![4, 3, 6, 16, 8, 2], 3), (vec![2, 3, 5, 6, 7], -1)];
+    println!("\n\x1b[92m» Running {} tests...\x1b[0m", tests.len());
+    let mut success = 0;
+    for (i, t) in tests.iter().enumerate() {
+        let res = Solution::longest_square_streak(t.0.clone());
+        if res == t.1 {
+            success += 1;
+            println!("\x1b[92m✔\x1b[95m Test {} passed!\x1b[0m", i);
+        } else {
+            println!(
+                "\x1b[31mx\x1b[95m Test {} failed expected: {:?} but got {}!!\x1b[0m",
+                i, t.1, res
+            );
+        }
+    }
+    println!();
+    if success == tests.len() {
+        println!("\x1b[30;42m✔ All tests passed!\x1b[0m")
+    } else if success == 0 {
+        println!("\x1b[31mx \x1b[41;37mAll tests failed!\x1b[0m")
+    } else {
+        println!(
+            "\x1b[31mx\x1b[95m {} tests failed!\x1b[0m",
+            tests.len() - success
+        )
+    }
+}