Disjoint-set (disjoint sets) operation Deunion

Additional operations disjoint-set (disjoint set) $Deunion$ , its function is to achieve undo the last $Union$ operation.

Realize ideas

Initialize an empty stack, each time $Union$ two root set of operations and the value $Push$ stack; if performed $Deunion$ operation, the stack only needs to be $Pop$ can operate. Nopath compressiontime, this strategy is valid; if disjoint-set (disjoint set) to achieve apath compression, such that the $Deunion$ operation difficult, since thepath compressora great probability originally belonging to the elements under a root connected to the other root, if performed at this time $Union$ operation, it is difficult to recover.