size (); ++ i ) { if ( i!= 0 && nums [ i ] == nums [ i - 1 ]) continue ; unordered_set < int > seen ; for ( int j = i + 1 ; j < nums.
push_back ({ nums [ i ], nums [ j ], - nums [ i ] - nums [ j ]}); // Skip duplicates while ( nums [ j + 1 ] == nums [ j ] && j + 1 < nums.