Given a string in which all decimals are concatenated , write a function to find the Nth character in the string.
Example
INPUT
s = “123456789101112131415…..”
OUTPUT
For N = 7, OUTPUT : 7
For N= 10, OUTPUT : 1
For N = 51, OUTPUT : 0
In this method the main idea is, considering the fact that in decimal 9 numbers are of length 1, 90 numbers are of length 2 and 900 numbers are of lengthh 3 and so on. So skip these numbers according to the given N and find the charcater
Algorithm
1. Find the length of the number at N
2. Now, get the character at N
Implementation of above algorithm
Example,
INPUT : N = 51
1) Finding the length of the number at N
51 – 9 = 42 // There are 9 numbers with length 1
42 – 90*2 < 0 // As there are 90 numbers with length 2, we got to know that the length is 2
2) Find the character at N
42 characters are after max 1 digit number(ie, 9)
ceil(42/2) = 21,so 9+21 = 30
30 is the number at N
Now, finding the actual character at N
42%2 = 0, so take 2nd digit of 30
Therefore, 0 is the character at N
C++ Program
#include <bits/stdc++.h>
using namespace std;
// To find the digit at N
char findDigit(int N, int d)
{
string s;
stringstream ss;
ss << N;
ss >> s;
return s[d - 1];
}
// Method to return Nth character in concatenated
// decimal string
char getNthChar(int N)
{
// no_of_chars will store character escaped till now
int no_of_chars = 0, nine = 9;
// no_of_nums will store numbers escaped till now
int no_of_nums = 0, len;
// loop for number lengths
for (len = 1; ; len++)
{
// increament with nine*len chars
no_of_chars += nine*len;
//increment with nine numbers
no_of_nums += nine;
if (no_of_chars >= N)
{
// restore variables to previous correct state
no_of_chars -= nine*len;
no_of_nums -= nine;
N -= no_of_chars;
break;
}
nine *= 10;
}
// differnce fomr las max digit
int diff = ceil((double)N / len);
// d will store dth digit of current number
int d = N % len;
cout<<d<<endl;
if (d == 0)
d = len;
cout<<d;
// method will return the digit at N
return getDigit(no_of_nums + diff, d);
}
int main()
{
int N = 51;
cout << getNthChar(N) << endl;
return 0;
}
