DAY 28
1
Software Development

原始題目

Given an array of integers `arr`, return `true` 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
`(arr[0] + arr[1] + ... + arr[i] == arr[i + 1] + arr[i + 2] + ... + arr[j - 1] == arr[j] + arr[j + 1] + ... + arr[arr.length - 1])`

Example 1:

``````Input: arr = [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: arr = [0,2,1,-6,6,7,9,-1,2,0,1]
Output: false
``````

Example 3:

``````Input: arr = [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 <= arr.length <= 5 * 104
• -104 <= arr[i] <= 104

解題過程

``````class Solution:
def canThreePartsEqualSum(self, arr: List[int]) -> bool:
s = sum(arr)
if s % 3 != 0:
return False

target = s // 3
n, i, cur = len(arr), 0, 0

while i < n:
cur += arr[i]
if cur == target:
break
i += 1

if cur != target:
return False

j = i + 1
while j + 1 < n:
cur += arr[j]
if cur == target * 2:
return True
j += 1

return False
``````