Connect all equal numbers with a line that only goes horizontally or vertically. Connections between distinct numbers are not allowed to cross each other, except at special bridges that appear in some puzzles. Connections are not allowed to pass through thicker borders and black cells.
Puzzles in this genre
To connect the 2's, we have the option to draw the line either through the lefthand part or through the righthand part of the diagram. However, if we pick the lefthand option, we will basically deny the 3 in the lower left any possibility to get in touch with the other 3. Also the 1's will get separated in this case. Therefore, we draw the line through the righthand side of the puzzle.
The only way to connect the remaining numbers is to take the shortest path between the 1's. Any other path prevents the 3's from connecting.