Generate Product Except Self % m(== f), add all of them, then % m(== g), return g

ProductExceptSelf.cs

int productExceptSelf(int[] nums, int m) {
    var query = from i in Enumerable.Repeat(1, nums.Length)
                select (Int64)i;
    Int64[] prefixProducts = query.ToArray();
    Int64[] postfixProducts = query.ToArray();
    
    // Generate f
    for (int i = 1; i < nums.Length; i++)
    {
        prefixProducts[i] = nums[i - 1] * prefixProducts[i - 1];
    }
    
    for (int i = nums.Length - 2; i >= 0; i--)
    {
        postfixProducts[i] = nums[i + 1] * postfixProducts[i + 1];
    }
    
    
    var FValues = prefixProducts.Zip(postfixProducts, (i, j) => i*j % m);
    
    // Debug print
    foreach (var i in FValues)
    {
        Console.Write($"{i}, ");
        
    }
    Console.WriteLine();
    
    var GValue = (int)FValues.Aggregate((sum, x) => sum + x);
    
    return GValue % m;
}