Recursively call for the list less than the last element and and return the newly formed list
vector < int > pass ; for ( int i = 0 ; i < res . size ( ) - 1 ; i ++ ) pass . push_back ( res [ i ] ) ; vector < int > ans = bubble_sort ( pass ) ; ans . push_back ( res [ res . size ( ) - 1 ] ) ; return ans ; }