1013. Partition Array Into Three Parts With Equal Sum

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

Rust Solution

struct Solution;

impl Solution {
    fn can_three_parts_equal_sum(a: Vec<i32>) -> bool {
        let total: i32 = a.iter().sum();
        let mut parts = 0;
        let mut sum = 0;
        if total % 3 != 0 {
            return false;
        }
        for x in a {
            sum += x;
            if sum == total / 3 {
                parts += 1;
                if parts == 2 {
                    return true;
                }
                sum = 0;
            }
        }
        false
    }
}

#[test]
fn test() {
    let a = vec![0, 2, 1, -6, 6, -7, 9, 1, 2, 0, 1];
    assert_eq!(Solution::can_three_parts_equal_sum(a), true);
    let a = vec![0, 2, 1, -6, 6, 7, 9, -1, 2, 0, 1];
    assert_eq!(Solution::can_three_parts_equal_sum(a), false);
    let a = vec![3, 3, 6, 5, -2, 2, 5, 1, -9, 4];
    assert_eq!(Solution::can_three_parts_equal_sum(a), true);
}

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