Eliminate Maximum Number of Monsters

CMakeLists.txt

@@ -276,6 +276,7 @@ add_task(duplicate-zeros)
 add_task(earliest-possible-day-of-full-bloom)
 add_task(edit-distance)
 add_task(element-appearing-more-than-25-in-sorted-array)
+add_task(eliminate-maximum-number-of-monsters)
 add_task(equal-row-and-column-pairs)
 add_task(evaluate-boolean-binary-tree)
 add_task(evaluate-division)

README.md

@@ -865,6 +865,7 @@ leetcode pull -d
 | 1909. | [Remove One Element to Make the Array Strictly Increasing](https://leetcode.com/problems/remove-one-element-to-make-the-array-strictly-increasing/) | [C++](./solutions/remove-one-element-to-make-the-array-strictly-increasing/solution.hpp) | <img src='https://img.shields.io/badge/Easy-darkgreen?style=flat-square'/> | | <img src='https://img.shields.io/badge/Array-57337f?style=flat-square'/> |  |
 | 1913. | [Maximum Product Difference Between Two Pairs](https://leetcode.com/problems/maximum-product-difference-between-two-pairs/) | [C++](./solutions/maximum-product-difference-between-two-pairs/solution.hpp) | <img src='https://img.shields.io/badge/Easy-darkgreen?style=flat-square'/> | | <img src='https://img.shields.io/badge/Array-57337f?style=flat-square'/> <img src='https://img.shields.io/badge/Sorting-333b7f?style=flat-square'/> |  |
 | 1920. | [Build Array from Permutation](https://leetcode.com/problems/build-array-from-permutation/) | [C++](./solutions/build-array-from-permutation/solution.hpp) | <img src='https://img.shields.io/badge/Easy-darkgreen?style=flat-square'/> | | <img src='https://img.shields.io/badge/Array-57337f?style=flat-square'/> <img src='https://img.shields.io/badge/Simulation-7e7f33?style=flat-square'/> |  |
+| 1921. | [Eliminate Maximum Number of Monsters](https://leetcode.com/problems/eliminate-maximum-number-of-monsters/) | [C++](./solutions/eliminate-maximum-number-of-monsters/solution.hpp) | <img src='https://img.shields.io/badge/Medium-darkorange?style=flat-square'/> | O(N) / O(N)| <img src='https://img.shields.io/badge/Array-57337f?style=flat-square'/> <img src='https://img.shields.io/badge/Greedy-44337f?style=flat-square'/> <img src='https://img.shields.io/badge/Sorting-333b7f?style=flat-square'/> |  |
 | 1925. | [Count Square Sum Triples](https://leetcode.com/problems/count-square-sum-triples/) | [C++](./solutions/count-square-sum-triples/solution.hpp) | <img src='https://img.shields.io/badge/Easy-darkgreen?style=flat-square'/> | | <img src='https://img.shields.io/badge/Math-7f5933?style=flat-square'/> <img src='https://img.shields.io/badge/Enumeration-7f7a33?style=flat-square'/> |  |
 | 1926. | [Nearest Exit from Entrance in Maze](https://leetcode.com/problems/nearest-exit-from-entrance-in-maze/) | [C++](./solutions/nearest-exit-from-entrance-in-maze/solution.hpp) | <img src='https://img.shields.io/badge/Medium-darkorange?style=flat-square'/> | | <img src='https://img.shields.io/badge/Array-57337f?style=flat-square'/> <img src='https://img.shields.io/badge/Breadth First Search-377f33?style=flat-square'/> <img src='https://img.shields.io/badge/Matrix-5e337f?style=flat-square'/> |  |
 | 1929. | [Concatenation of Array](https://leetcode.com/problems/concatenation-of-array/) | [C++](./solutions/concatenation-of-array/solution.hpp) | <img src='https://img.shields.io/badge/Easy-darkgreen?style=flat-square'/> | | <img src='https://img.shields.io/badge/Array-57337f?style=flat-square'/> |  |

solutions/eliminate-maximum-number-of-monsters/CMakeLists.txt

@@ -0,0 +1 @@
+add_catch(test_eliminate_maximum_number_of_monsters test.cpp)

solutions/eliminate-maximum-number-of-monsters/solution.hpp

@@ -0,0 +1,65 @@
+#pragma once
+
+#include <numeric>
+#include <ranges>
+#include <vector>
+
+// Time: O(N)
+// Space: O(N)
+
+namespace sorting {
+
+// Time: O(NlogN)
+// Space: O(N)
+class Solution {
+public:
+  static int eliminateMaximum(const std::vector<int> &dist,
+                              const std::vector<int> &speed) {
+    const int n = dist.size();
+
+    std::vector<int> arrival(n);
+    for (int i = 0; i < n; ++i) {
+      arrival[i] = (dist[i] + speed[i] - 1) / speed[i];
+    }
+    std::ranges::sort(arrival);
+
+    for (int i = 0; i < n; ++i) {
+      if (i >= arrival[i]) {
+        return i;
+      }
+    }
+    return n;
+  }
+};
+
+} // namespace sorting
+
+namespace counting {
+
+// Time: O(N)
+// Space: O(N)
+class Solution {
+public:
+  static int eliminateMaximum(const std::vector<int> &dist,
+                              const std::vector<int> &speed) {
+    const int n = dist.size();
+
+    std::vector<int> counter(n);
+    for (int i = 0; i < n; ++i) {
+      const auto arrival = (dist[i] + speed[i] - 1) / speed[i];
+      if (arrival < n) {
+        ++counter[arrival];
+      }
+    }
+    std::partial_sum(counter.cbegin(), counter.cend(), counter.begin());
+
+    for (int i = 0; i < n; ++i) {
+      if (counter[i] > i) {
+        return i;
+      }
+    }
+    return n;
+  }
+};
+
+} // namespace counting

solutions/eliminate-maximum-number-of-monsters/test.cpp

@@ -0,0 +1,43 @@
+#include <catch.hpp>
+
+#include <solution.hpp>
+
+TEST_CASE("Simple") {
+  struct TestCase {
+    std::vector<int> dist;
+    std::vector<int> speed;
+    int expected;
+  };
+
+  std::vector<TestCase> test_cases{
+      {
+          .dist{1, 3, 4},
+          .speed{1, 1, 1},
+          .expected = 3,
+      },
+      {
+          .dist{1, 1, 2, 3},
+          .speed{1, 1, 1, 1},
+          .expected = 1,
+      },
+      {
+          .dist{3, 2, 4},
+          .speed{5, 3, 2},
+          .expected = 1,
+      },
+  };
+
+  SECTION("Sorting") {
+    for (const auto &[dist, speed, expected] : test_cases) {
+      const auto actual = sorting::Solution::eliminateMaximum(dist, speed);
+      REQUIRE(expected == actual);
+    }
+  }
+
+  SECTION("Counting") {
+    for (const auto &[dist, speed, expected] : test_cases) {
+      const auto actual = counting::Solution::eliminateMaximum(dist, speed);
+      REQUIRE(expected == actual);
+    }
+  }
+}