The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other.

Given an integer n, return the number of distinct solutions to the n-queens puzzle.

This is my code for the n queens question. I cant find any error but my output keeps coming out to be 0. pls help

class Solution 
{
    public int totalNQueens(int n)
 {
        List<List<Integer>> result=new ArrayList<>();
        function(n,0,result,new ArrayList<Integer>());
        return result.size();
    }
    
    
  public void function(int n, int row,List<List<Integer>> result,List<Integer> col)
    {
        if(n==row)
        {
            result.add(new ArrayList<>(col));
        }
        else
        {
            for(int i=0;i<n;i++)
            {
                col.add(i);
                if(isvalid(col))
                {
                 function(n,row+1,result,col);
                }
                else
                    col.remove(col.size()-1);
            }
        }
    }
    
    
    public boolean isvalid(List<Integer> col)
    {
        // if(col.size()==1)
        //     return true;
        // int c=col.get(col.size()-1);
        int r=col.size()-1;
        for(int i=0;i<r;i++)
        {
            if(col.get(r)==col.get(i) || Math.abs(i-r)==Math.abs(col.get(r)-col.get(i)))
                return false;
        }
        return true;
    }
}