Partition Array Into Three Parts With Equal Sum

EasyArrays & Hashingprefix sum

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

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Problem

Given an integer array arr, decide whether it can be cut into three **non-empty contiguous** pieces whose sums are all equal. Formally, return true if there exist indices i and j with 0 < i < j < arr.length such that arr[0] + ... + arr[i-1], arr[i] + ... + arr[j-1], and arr[j] + ... + arr[arr.length-1] are all the same value. Otherwise return false. Aim for a single O(n) pass.

Examples

Input: arr = [0,2,1,-6,6,-7,9,1,2,0,1]
Output: true
Pieces `[0,2,1]`, `[-6,6,-7,9,1]`, `[2,0,1]` each sum to 3.
Input: arr = [0,2,1,-6,6,7,9,-1,2,0,1]
Output: false
The total is 21, so each piece would need sum 7, and no valid pair of cuts achieves that.
Input: arr = [3,3,6,5,-2,2,5,1,-9,4]
Output: true
Pieces `[3,3]`, `[6]`, `[5,-2,2,5,1,-9,4]` each sum to 6.

Constraints

  • 3 <= arr.length <= 5 * 10^4
  • -10^4 <= arr[i] <= 10^4

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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