int main()
{
int n;
printf("input a number: n=");
scanf("%d", &n);
printf("the number of 1 is: %d\n", NumberOf1(n));
}
int NumberOf1(string str) {
if (str.empty())
return 0;
int first = str[0] - '0';
int length = str.size();
if (length == 1 && first == 0)
return 0;
if (length == 1 && first >= 1)
return 1;
int numFirstDigit = 0;
if (first > 1)
numFirstDigit = pow(10, length - 1);
else if (first == 1)
numFirstDigit = stoi(str.substr(1)) + 1;
int numOtherdigits = first * (length - 1)* pow(10, length - 2);
int numRecursive = NumberOf1(str.substr(1));
return numFirstDigit + numOtherdigits + numRecursive;
}
int countDigitOne(int n) {
if (n <= 0)
return 0;
string str = to_string(n);
return NumberOf1(str);
}
int main(int argc, char *argv[])
{
int n = atoi(argv[1]);
printf("%d %d\n",NumberOf1_Regular(n),NumberOf1(n));
return 0;
}
