Given a non-negative integer represented as a non-empty array of digits, plus one to the integer.
You may assume the integer do not contain any leading zero, except the number 0 itself.
The digits are stored such that the most significant digit is at the head of the list.
解法：
func plusOne(digits []int) []int {
carry, sum, n := 1, 0, len(digits)
for i := n-1; i >= 0; i-- {
if digits[i] < 9 {
digits[i] = (digits[i] + carry)
return digits
} else {
sum = digits[i] + carry
carry = sum / 10
digits[i] = sum % 10
}
}
if carry == 1 {
digits = append([]int{1}, digits...)
}
return digits
}