C++ Program:

Example:

    1
  1 2 1
1 2 3 2 1

#include <iostream>
using namespace std;

int main() {
  int rows,k;
  cout <<"Enter number of rows: ";
  cin >> rows;
  for(int i=rows; i>=1; i--) {
    k=1;
    for(int j=1; j<=(2*rows-i); j++) {
      if(j<i)cout<<"  ";
      else {
        if(j<rows)cout<<k++<<" ";
        else cout<<k--<<" ";
      }
    }
    cout<<endl;
  }
  return 0;
}

Output:

Enter number of rows: 4

      1
    1 2 1
  1 2 3 2 1
1 2 3 4 3 2 1

Main Logic :

for(int i=rows; i>=1; i--) {
  k=1;
  for(int j=1; j<=(2*rows-i); j++) {
    if(j<i)cout<<"  ";
    else {
      if(j<rows)cout<<k++<<" ";
      else cout<<k--<<" ";
    }
  }
  cout<<endl;
}