hourglass O(n)

hourglass.go

func hourglassSum(arr [][]int32) int32 {
    var maxVal int32 = -63
    for i, j := 0, 0; i < len(arr) - 2; j++ {
        tr := arr[i][j] + arr[i][j+1] + arr[i][j+2]
        mr := arr[i+1][j+1]
        br := arr[i+2][j] + arr[i+2][j+1] + arr[i+2][j+2]
        total := tr + mr + br
        if total > maxVal {
            maxVal = total
        }
        if j == len(arr[i]) - 3 {
            i += 1
            j = -1
        }
    } 
    return maxVal
}