410. Split Array Largest Sum

func splitArray(_ nums: [Int], _ m: Int) -> Int {
        var endSum = 0
        var startSum = Int.max
        for n in nums {
            startSum = min( startSum , n)
            endSum += n
        }

        while startSum + 1 < endSum{
            let mid = (startSum + endSum) / 2
            if !canCountWithSum(nums, mid, m){
                startSum = mid
            }else{
                endSum = mid
            }
        }
        if canCountWithSum(nums, endSum, m) { return endSum}
        return startSum
    }



    func canCountWithSum(_ nums: [Int], _ sum: Int, _ k: Int) -> Bool{
        var curS = 0
        var count = 1
        for n in nums{
            if curS + n > sum{
                count += 1
                curS = n
                if curS > sum || count > k {
                    return false
                }
            }else{
                curS += n
            }
        }
        return true
    }