Implement task-scheduler

name: task-scheduler
url: https://leetcode.com/problems/task-scheduler
difficulty: medium

time: 132ms
time-rank: 48.86%
time-complexity: O(N)

space: 34.9MB
space-rank: 66.22%
space-complexity: O(1)

Fixes #271

Signed-off-by: Christopher Friedt <[email protected]>

Author: cfriedt

task-scheduler-test.cpp

@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2021, Christopher Friedt
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <gtest/gtest.h>
+
+#include "task-scheduler.cpp"
+
+using namespace std;
+
+TEST(TaskScheduler, AAABBB_2) {
+  vector<char> tasks = {'A', 'A', 'A', 'B', 'B', 'B'};
+  int n = 2;
+  EXPECT_EQ(8, Solution().leastInterval(tasks, n));
+}
+
+TEST(TaskScheduler, AAABBB_0) {
+  vector<char> tasks = {'A', 'A', 'A', 'B', 'B', 'B'};
+  int n = 0;
+  EXPECT_EQ(6, Solution().leastInterval(tasks, n));
+}
+
+TEST(TaskScheduler, AAAAAABCDEFG_2) {
+  vector<char> tasks = {'A', 'A', 'A', 'A', 'A', 'A',
+                        'B', 'C', 'D', 'E', 'F', 'G'};
+  int n = 2;
+  EXPECT_EQ(16, Solution().leastInterval(tasks, n));
+}
+
+TEST(TaskScheduler, AAABBB_50) {
+  vector<char> tasks = {'A', 'A', 'A', 'B', 'B', 'B'};
+  int n = 50;
+  EXPECT_EQ(104, Solution().leastInterval(tasks, n));
+}
+
+TEST(TaskScheduler, AAABBBCCCDDE_2) {
+  vector<char> tasks = {'A', 'A', 'A', 'B', 'B', 'B',
+                        'C', 'C', 'C', 'D', 'D', 'E'};
+  int n = 2;
+  EXPECT_EQ(12, Solution().leastInterval(tasks, n));
+}
+
+TEST(TaskScheduler, AABCDEFGHIJKLMNOPQRSTUVWXYZ_2) {
+  vector<char> tasks = {'A', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
+                        'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q',
+                        'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'};
+  int n = 31;
+  EXPECT_EQ(33, Solution().leastInterval(tasks, n));
+}
+
+TEST(TaskScheduler, ABCDEABCDE_4) {
+  vector<char> tasks = {'A', 'B', 'C', 'D', 'E', 'A', 'B', 'C', 'D', 'E'};
+  int n = 4;
+  EXPECT_EQ(10, Solution().leastInterval(tasks, n));
+}
+
+TEST(TaskScheduler, ABCDEFGHIJKLMNOPQRSTUVWXYZ_15) {
+  vector<char> tasks = {
+'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
+'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
+'U', 'V', 'W', 'X', 'Y', 'Z'
+  };
+  int n = 15;
+  EXPECT_EQ(26, Solution().leastInterval(tasks, n));
+}

task-scheduler.cpp

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2021, Christopher Friedt
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <algorithm>
+#include <unordered_map>
+#include <vector>
+
+using namespace std;
+
+// name: task-scheduler
+// url: https://leetcode.com/problems/task-scheduler
+// difficulty: 2
+
+class Solution {
+public:
+  int leastInterval(vector<char> &tasks, int n) {
+    if (0 == n) {
+      return tasks.size();
+    }
+
+    unordered_map<char, int> hist;
+    int peak = 0;
+    // create a histogram of task frequencies, also keep track of peak frequency
+    for (const auto &task : tasks) {
+      hist[task]++;
+      peak = max(peak, hist[task]);
+    }
+
+    if (hist.size() == tasks.size()) {
+      return tasks.size();
+    }
+
+    // find the number of tasks that share the peak frequency
+    int npeak = 0;
+    for (auto &kv : hist) {
+      if (kv.second == peak) {
+        ++npeak;
+      }
+    }
+
+    return max(int(tasks.size()), (peak - 1) * (n + 1) + npeak);
+  }
+};