1013 Partition Array Into Three Parts With Equal Sum.py

Author: rajeevranjancom

1013 Partition Array Into Three Parts With Equal Sum.py

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+#!/usr/bin/python3
+"""
+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:
+
+3 <= A.length <= 50000
+-10000 <= A[i] <= 10000
+"""
+from typing import List
+
+
+class Solution:
+    def canThreePartsEqualSum(self, A: List[int]) -> bool:
+        s = sum(A)
+        if s % 3 != 0:
+            return False
+
+        target = s // 3
+        count = 0
+        cur_sum = 0
+        for a in A:
+            cur_sum += a
+            if cur_sum == target:
+                count += 1
+                cur_sum = 0
+            # elif cur_sum > target:
+            #     return False
+            # can have negative number 
+
+        return count == 3 and cur_sum == 0
+
+
+if __name__ == "__main__":
+    assert Solution().canThreePartsEqualSum([3,3,6,5,-2,2,5,1,-9,4]) == True