# Lexicographical Numbers in C++

C++Server Side ProgrammingProgramming

Suppose we have an integer n. We have to return 1 to n in lexicographic order. So for example when 13 is given, then the output will be [1, 10, 11, 12, 13, 2, 3, 4, 5, 6, 7, 8, 9].

To solve this, we will follow these steps −

• define one array ret of size n

• curr := 1

• for i in range 0 to n – 1

• ret[i] := curr

• if curr * 10 <= n, then set curr := curr * 10

• otherwise

• if curr >= n, then curr := curr / 10

• increase curr by 1

• while curr is divisible by 10, then curr := curr / 10

• return ret

## Example(C++)

Let us see the following implementation to get better understanding −

Live Demo

#include <bits/stdc++.h>
using namespace std;
void print_vector(vector<auto> v){
cout << "[";
for(int i = 0; i<v.size(); i++){
cout << v[i] << ", ";
}
cout << "]"<<endl;
}
class Solution {
public:
vector<int> lexicalOrder(int n) {
vector <int> ret(n);
int curr = 1;
for(int i = 0; i < n; i++){
ret[i] = curr;
if(curr * 10 <= n){
curr*= 10;
} else {
if(curr>= n)curr /= 10;
curr += 1;
while(curr % 10 == 0)curr/=10;
}
}
return ret;
}
};
main(){
Solution ob;
print_vector(ob.lexicalOrder(20));
}

## Input

20

## Output

[1, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 2, 20, 3, 4, 5, 6, 7, 8, 9, ]