Task Scheduler - Implementation

function leastInterval(tasks, n)
 count := array of 26 zeros
 for each task in tasks
 count[task - 'A'] := count[task - 'A'] + 1
 maxFreq := max of count
 maxCount := number of elements in count equal to maxFreq
 return max(length of tasks, (maxFreq - 1) * (n + 1) + maxCount)

Time: $O(n)$. Space: $O(1)$ ($26$ letters).