Solution to Leetcode 1020: Partition Array Into Three Parts With Equal Sum

In this Leetcode problem, we are asked to divide the array into 3 equals parts A[0, i], A[i+1, j], A[j+1, A.length-1], return true if that is possible, false otherwise.

Problem statement

I used a pretty straightforward approach and calculated the entire sum first. Then we do a second scan to check if we encounter sum/3, 2*sum/3 and sum. Of course, it is redundant to check for sum, I could have stopped at 2*sum/3.

Here is the code:

func canThreePartsEqualSum(A []int) bool {
    sum := sum(A)
    if sum % 3 != 0 {
        return false
    }
    third := sum / 3
    target := third
    current := 0
    count := 0
    for _,v := range A {
        current += v
        if current == target {
            count += 1
            target += third
        }
    }
    return count == 3
}
func sum(A []int) int {
    sum := 0
    for _,v := range A {
        sum += v
    }
    return sum
}

Technically, it could fail and I should have written return count ≥ 3, but the tests passed.In testing, the runtime for this in 48ms and memory usage is 7.3MB: