## Problem

### Description

Given a char array representing tasks CPU need to do. It contains capital letters A to Z where different letters represent different tasks.Tasks could be done without original order. Each task could be done in one interval. For each interval, CPU could finish one task or just be idle.

However, there is a non-negative cooling interval n that means between two same tasks, there must be at least n intervals that CPU are doing different tasks or just be idle.

You need to return the least number of intervals the CPU will take to finish all the given tasks.

#### Notice

1. The number of tasks is in the range [1, 10000].
2. The integer n is in the range [0, 100].

#### Example

Given tasks = ['A','A','A','B','B','B'], n = 2, return 8.

Explanation:
A -> B -> idle -> A -> B -> idle -> A -> B.


## 题解 - 填充空闲时隙

TODO 分情况讨论

1. 出现频率最高的字符有多个
2. 以频率最高的字符为分界点，空闲时隙数不够所有字符放满
3. 空闲时隙数足够所有字符放下

### Java

class Solution {
public int leastInterval(char[] tasks, int n) {
if (tasks == null) return -1;

int[] map = new int[26];
for (char c : tasks) {
map[c - 'A']++;
}
Arrays.sort(map);

int maxFreq = map[25];
int idleSlots = n * (maxFreq - 1);
for (int i = 24; i >= 0; i--) {
if (map[i] == 0) {
break;
} else if (map[i] == maxFreq) {
idleSlots -= maxFreq - 1;
} else {
idleSlots -= map[i];
}
}

}
}


## Reference

Task Scheduler - Approach #3 Calculating Idle slots