Big O Notation help

[tm70]

Algorithm of:

for ( j = 0; j < n; j++ )

{

for ( k = j; k < n; k++ )

{

<some operation>

}

}
will result in a number of iterations of <some operation> given by the expression:

<number of iterations> = n + (n-1) + (n-2) + (n-3) + ........ + (n - n)

Reduce the above series expression to an algebraic expression.

After determining the algebraic expression express the performance in Big O Notation.

[htirwin]

I will give you a hint.

    n + (n-1) + (n-2) + (n-3) + ... + 1
  + 1 +    2  +    3  +    4  + ... + n

= ?

What is n + (n-1) + (n-2) + (n-3) + ... + 1 in terms of ?