LC 42. Trapping Rain Water (Rust TP)

README.md

@@ -51,7 +51,7 @@ Solutions to LeetCode problems. The first column links to the problem in LeetCod
 | [39. Combination Sum][lc39]                                                                   | 🟠 Medium  | [![python](res/py.png)][lc39py]                                                                       |
 | [40. Combination Sum II][lc40]                                                                | 🟠 Medium  | [![python](res/py.png)][lc40py]                                                                       |
 | [41. First Missing Positive][lc41]                                                            | 🔴 Hard    | [![python](res/py.png)][lc41py] [![rust](res/rs.png)][lc41rs]                                         |
-| [42. Trapping Rain Water][lc42]                                                               | 🔴 Hard    | [![python](res/py.png)][lc42py]                                                                       |
+| [42. Trapping Rain Water][lc42]                                                               | 🔴 Hard    | [![python](res/py.png)][lc42py] [![rust](res/rs.png)][lc42rs]                                         |
 | [43. Multiply Strings][lc43]                                                                  | 🟠 Medium  | [![python](res/py.png)][lc43py]                                                                       |
 | [45. Jump Game II][lc45]                                                                      | 🟠 Medium  | [![python](res/py.png)][lc45py] [![rust](res/rs.png)][lc45rs]                                         |
 | [46. Permutations][lc46]                                                                      | 🟠 Medium  | [![python](res/py.png)][lc46py]                                                                       |
@@ -783,6 +783,7 @@ Solutions to LeetCode problems. The first column links to the problem in LeetCod
 [lc41rs]: leetcode/first-missing-positive.rs
 [lc42]: https://leetcode.com/problems/trapping-rain-water/
 [lc42py]: leetcode/trapping-rain-water.py
+[lc42rs]: leetcode/trapping-rain-water.rs
 [lc43]: https://leetcode.com/problems/multiply-strings/
 [lc43py]: leetcode/multiply-strings.py
 [lc45]: https://leetcode.com/problems/jump-game-ii/

leetcode/trapping-rain-water.rs

@@ -0,0 +1,105 @@
+// 42. Trapping Rain Water
+// 🔴 Hard
+//
+// https://leetcode.com/problems/trapping-rain-water/
+//
+// Tags: Array - Two Pointers - Dynamic Programming - Stack - Monotonic Stack
+
+struct Solution;
+impl Solution {
+    /// Use two pointers, the minimum height between them is the maximum water that we will be able
+    /// to collect if some of the bars between them have a lower height.
+    ///
+    /// Time complexity: O(n) - We visit each position in the input once and do O(1) work for each.
+    /// Space complexity: O(1) - We store several integers.
+    ///
+    /// Runtime 2 ms Beats 72%
+    /// Memory 2.22 MB Beats 57%
+    #[allow(dead_code)]
+    pub fn trap_if(height: Vec<i32>) -> i32 {
+        let (mut water_trapped, mut l, mut r) = (0, 0, height.len() - 1);
+        let (mut max_left, mut max_right) = (height[l], height[r]);
+        while l + 1 < r {
+            if max_left < max_right {
+                l += 1;
+                if height[l] > max_left {
+                    max_left = height[l];
+                } else if height[l] < max_left {
+                    water_trapped += max_left - height[l];
+                }
+            } else {
+                r -= 1;
+                if height[r] > max_right {
+                    max_right = height[r];
+                } else if height[r] < max_right {
+                    water_trapped += max_right - height[r];
+                }
+            }
+        }
+        water_trapped
+    }
+
+    /// Same solution but use cmp.
+    ///
+    /// Time complexity: O(n) - We visit each position in the input once and do O(1) work for each.
+    /// Space complexity: O(1) - We store several integers.
+    ///
+    /// Runtime 2 ms Beats 72%
+    /// Memory 2.22 MB Beats 57%
+    pub fn trap(height: Vec<i32>) -> i32 {
+        let (mut water_trapped, mut l, mut r) = (0, 0, height.len() - 1);
+        let (mut max_left, mut max_right) = (height[l], height[r]);
+        while l + 1 < r {
+            if max_left < max_right {
+                l += 1;
+                match max_left.cmp(&height[l]) {
+                    std::cmp::Ordering::Less => max_left = height[l],
+                    std::cmp::Ordering::Equal => (),
+                    std::cmp::Ordering::Greater => water_trapped += max_left - height[l],
+                }
+            } else {
+                r -= 1;
+                match max_right.cmp(&height[r]) {
+                    std::cmp::Ordering::Less => max_right = height[r],
+                    std::cmp::Ordering::Equal => (),
+                    std::cmp::Ordering::Greater => water_trapped += max_right - height[r],
+                }
+            }
+        }
+        water_trapped
+    }
+}
+
+// Tests.
+fn main() {
+    let tests = [
+        (vec![0], 0),
+        (vec![4, 2, 0, 3, 2, 5], 9),
+        (vec![0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1], 6),
+    ];
+    println!("\n\x1b[92m» Running {} tests...\x1b[0m", tests.len());
+    let mut success = 0;
+    for (i, t) in tests.iter().enumerate() {
+        let res = Solution::trap(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
+        )
+    }
+}