The first thing you will see when you enter the world of Minecraft Pocket Edition – witch's hut. Seeds of this kind is quite rare, but they exist. However, this is one of those rare seeds, thanks to which you will meet the witch's cottage.
When you will enter the world of MCPE, you will see a witch's hut. In the game settings enable the maximum complexity of the game, so she could appear independently in the world. If the witch is not detected, try to restart the game, then re-enter the seed. Sometimes after re-entry, witches may appear.
As usual, the witch hut is generated near the swamps, in this case, all the same. Near the swamp biome you will encounter and plains biome.