Leetcode

1020. Partition Array Into Three Parts With Equal Sum

Given an array A of integers, return true if and only if we can partition the array into three non-empty parts with equal sums.

Formally, we can partition the array if we can find indexes i+1 < j with (A[0] + A[1] + ... + A[i] == A[i+1] + A[i+2] + ... + A[j-1] == A[j] + A[j-1] + ... + A[A.length - 1])

 

Example 1:

Input: 

[0,2,1,-6,6,-7,9,1,2,0,1]

Output: 

true
Explanation: 0 + 2 + 1 = -6 + 6 - 7 + 9 + 1 = 2 + 0 + 1

Example 2:

Input: 

[0,2,1,-6,6,7,9,-1,2,0,1]

Output: 

false

Example 3:

Input: 

[3,3,6,5,-2,2,5,1,-9,4]

Output: 

true
Explanation: 3 + 3 = 6 = 5 - 2 + 2 + 5 + 1 - 9 + 4

 

Note:

  1. 3 <= A.length <= 50000
  2. -10000 <= A[i] <= 10000
class Solution {

    /**
     * @param Integer[] $A
     * @return Boolean
     */
    function canThreePartsEqualSum($A) {
        $mean = array_sum($A) / 3;
        if (floor($mean) != $mean){
            return false;
        }
        
        $count  = 0;
        $sum = 0;
        $i = 0;
        while ($i < count($A)){    
            $sum += $A[$i];
            $i ++;
            if($sum == $mean){
                $count ++;
                $sum = 0;
            }
        }
        return $count == 3;
    }
}