CountTriangles function
void CountTriangles ( vector < int > A ) { int n = A . size ( ) ; sort ( A . begin ( ) , A . end ( ) ) ; int count = 0 ; for ( int i = n - 1 ; i >= 1 ; i -- ) { int l = 0 , r = i - 1 ; while ( l < r ) { if ( A [ l ] + A [ r ] > A [ i ] ) {