C++ To Infinity | AtCoder

Problem Statement

Mr. Infinity has a string S consisting of digits from 1 to 9. Each time the date changes, this string changes as follows:

• Each occurrence of 2 in SS is replaced with 22. Similarly, each 3 becomes 333, 4 becomes 4444, 5 becomes 55555, 6 becomes 666666, 7 becomes 7777777, 8 becomes 88888888 and 9 becomes 999999999. 1 remains as 1.

For example, if SS is 1324, it becomes 1333224444 the next day, and it becomes 133333333322224444444444444444 the day after next. You are interested in what the string looks like after  5×10^15 days. What is the K-th character from the left in the string after  5×10^15 days?

Input

S
K

Output

Print the K-th character from the left in Mr. Infinity's string after 5×10^15 days.

2

The string S changes as follows:

• Now: 1214
• After one day: 12214444
• After two days: 1222214444444444444444
• After three days: 12222222214444444444444444444444444444444444444444444444444444444444444444

The first five characters in the string after 5×10^15 days is 12222. As K=4, we should print the fourth character, 2.

Constraints

• S is a string of length between 1 and 100 (inclusive).
• K is an integer between 1 and 10^18 (inclusive).
• The length of the string after 5×10^15 days is at least K.

解题:

#include
using namespace std;
long long k,cnt;
string s;
int main(){
  	cin>>s>>k;
  	for(int i=0;isize();i++) {
    	if(s[i]!='1')break;
    	cnt++;
  	}
  	if(k<=cnt)printf("1");
  	else printf("%c",s[cnt]);
  	return 0;
}