/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func getDecimalValue(head *ListNode) int {
    sum := 0
    for head != nil {
        sum = sum * 2 + head.Val
        head = head.Next
    }
    return sum
}

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func getDecimalValue(head *ListNode) int {
    if head == nil {
        return 0
    }
    var s []int
    for head != nil {
        s = append(s, head.Val)
        head = head.Next
    }
    n := len(s)
    length := len(s)
    sum := 0
    for n > 0 {
        if s[n - 1] == 1 {
            sum += int(math.Pow(2, float64(length - n)))
        }
        n--
    }
    return sum
}