[LeetCode]1013. 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: A = [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: A = [0,2,1,-6,6,7,9,-1,2,0,1]
Output: false
Example 3:

Input: A = [3,3,6,5,-2,2,5,1,-9,4]
Output: true
Explanation: 3 + 3 = 6 = 5 - 2 + 2 + 5 + 1 - 9 + 4
 

Constraints:

3 <= A.length <= 50000
-10^4 <= A[i] <= 10^4

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/partition-array-into-three-parts-with-equal-sum
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python3:

 1 class Solution:
 2     def canThreePartsEqualSum(self, A: List[int]) -> bool:
 3         if sum(A) % 3 != 0:
 4             return False
 5         
 6         avg = sum(A) // 3
 7         i = 0
 8         j = len(A) - 1
 9         sum_f = A[i]
10         i += 1
11         sum_b = A[j]
12         j -= 1
13         rst = False
14         
15         while i < j:
16             if sum_f != avg:
17                 sum_f += A[i]
18                 i += 1
19             if sum_b != avg:
20                 sum_b += A[j]
21                 j -= 1
22             if sum_f == avg and sum_b == avg:
23                 rst = True
24                 break
25         
26         if i > j:
27             rst = False
28         return rst