LC 1326. Minimum Number of Taps to Open to Water a Garden (Rust Greedy)

Author: raul-sauco

README.md

@@ -425,6 +425,7 @@ Solutions to LeetCode problems. The first column links to the problem in LeetCod
 | [1318. Minimum Flips to Make a OR b Equal to c][lc1318]                                       | 🟠 Medium  | [![python](res/py.png)][lc1318py] [![rust](res/rs.png)][lc1318rs]                                     |
 | [1319. Number of Operations to Make Network Connected][lc1319]                                | 🟠 Medium  | [![python](res/py.png)][lc1319py] [![rust](res/rs.png)][lc1319rs] [![java](res/java.png)][lc1319java] |
 | [1323. Maximum 69 Number][lc1323]                                                             | 🟠 Medium  | [![python](res/py.png)][lc1323py]                                                                     |
+| [1326. Minimum Number of Taps to Open to Water a Garden][lc1326]                              | 🔴 Hard    | [![rust](res/rs.png)][lc1326rs]                                                                       |
 | [1328. Break a Palindrome][lc1328]                                                            | 🟠 Medium  | [![python](res/py.png)][lc1328py]                                                                     |
 | [1329. Sort the Matrix Diagonally][lc1329]                                                    | 🟠 Medium  | [![python](res/py.png)][lc1329py]                                                                     |
 | [1332. Remove Palindromic Subsequences][lc1332]                                               | 🟢 Easy    | [![python](res/py.png)][lc1332py]                                                                     |
@@ -1491,6 +1492,8 @@ Solutions to LeetCode problems. The first column links to the problem in LeetCod
 [lc1319rs]: leetcode/number-of-operations-to-make-network-connected.rs
 [lc1323]: https://leetcode.com/problems/maximum-69-number/
 [lc1323py]: leetcode/maximum-69-number.py
+[lc1326]: https://leetcode.com/problems/minimum-number-of-taps-to-open-to-water-a-garden/
+[lc1326rs]: leetcode/minimum-number-of-taps-to-open-to-water-a-garden.rs
 [lc1328]: https://leetcode.com/problems/break-a-palindrome/
 [lc1328py]: leetcode/break-a-palindrome.py
 [lc1329]: https://leetcode.com/problems/sort-the-matrix-diagonally/

leetcode/minimum-number-of-taps-to-open-to-water-a-garden.rs

@@ -0,0 +1,56 @@
+// 1326. Minimum Number of Taps to Open to Water a Garden
+// 🔴 Hard
+//
+// https://leetcode.com/problems/minimum-number-of-taps-to-open-to-water-a-garden/
+//
+// Tags: Array - Dynamic Programming - Greedy
+
+struct Solution;
+impl Solution {
+    /// Using an auxiliary vector that stores the max reach of each tap, we can
+    /// convert this problem to jump game 2, then visit each position and check
+    /// if we can reach it and if we need to add a "jump" to reach it.
+    ///
+    /// Time complexity: O(n) - We iterate twice over all elements of the input
+    /// and, both times, we do constant time work for each.
+    /// Space complexity: O(n) - The auxiliary max_reach vector has size n.
+    ///
+    /// Runtime 0 ms Beats 100%
+    /// Memory 2.44 MB Beats 20%
+    pub fn min_taps(n: i32, ranges: Vec<i32>) -> i32 {
+        let n = n as usize;
+        let mut max_reach = vec![0; n + 1];
+        let (mut start, mut end);
+        for i in 0..n + 1 {
+            start = 0.max(i as i32 - ranges[i]) as usize;
+            end = n.min(i + ranges[i] as usize);
+            max_reach[start] = max_reach[start].max(end);
+        }
+        let mut taps = 0;
+        let (mut curr_end, mut next_end) = (0, 0);
+        for i in 0..n + 1 {
+            if i > next_end {
+                return -1;
+            }
+            if i > curr_end {
+                taps += 1;
+                curr_end = next_end;
+            }
+            next_end = next_end.max(max_reach[i]);
+        }
+        taps
+    }
+}
+
+// Tests.
+fn main() {
+    let tests = [
+        (3, vec![0, 0, 0, 0], -1),
+        (5, vec![3, 4, 1, 1, 0, 0], 1),
+        (7, vec![1, 2, 1, 0, 2, 1, 0, 1], 3),
+    ];
+    for t in tests {
+        assert_eq!(Solution::min_taps(t.0, t.1), t.2);
+    }
+    println!("\x1b[92m» All tests passed!\x1b[0m")
+}