517. Super Washing Machines

1. Question

You have n super washing machines on a line. Initially, each washing machine has some dresses or is empty.

For each move, you could choose any m (1 <= m <= n) washing machines, and pass one dress of each washing machine to one of its adjacent washing machines at the same time.

Given an integer array machines representing the number of dresses in each washing machine from left to right on the line, return the minimum number of moves to make all the washing machines have the same number of dresses. If it is not possible to do it, return -1.

2. Examples

Example 1:

Input: machines = [1,0,5]
Output: 3
Explanation:
1st move:    1     0 <-- 5    =>    1     1     4
2nd move:    1 <-- 1 <-- 4    =>    2     1     3
3rd move:    2     1 <-- 3    =>    2     2     2

Example 2:

Input: machines = [0,3,0]
Output: 2
Explanation:
1st move:    0 <-- 3     0    =>    1     2     0
2nd move:    1     2 --> 0    =>    1     1     1

Example 3:

Input: machines = [0,2,0]
Output: -1
Explanation:
It's impossible to make all three washing machines have the same number of dresses.

3. Constraints

• n == machines.length
• 1 <= n <= 10⁴
• 0 <= machines[i] <= 10⁵

4. References

来源：力扣（LeetCode） 链接：https://leetcode-cn.com/problems/super-washing-machines 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

5. Solutions

一次只能换一件衣服，但是可以多台洗衣机同时换。所以本质上是一个求最大值的操作。

class Solution {
  public int findMinMoves(int[] machines) {
    int sum = Arrays.stream(machines).sum();
    if (sum % machines.length != 0) {
      return -1;
    }
    int avg = sum / machines.length;
    int ans = 0;
    int total = 0;

    for (int num : machines) {
      num -= avg;
      total += num;
      ans = Math.max(ans, Math.max(num, Math.abs(total)));
    }
    return ans;
  }
}