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Emil J. Tywoniak 2024-07-18 16:02:11 +02:00
parent a84e4f44fe
commit 583db7b15e
2 changed files with 28 additions and 0 deletions
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16
kernel/hashlib.h
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@ -1129,6 +1129,11 @@ public:
const_iterator end() const { return const_iterator(*this, offset + size()); }
};
/**
* Union-find data structure with a promotion method
* mfp stands for "merge, find, promote"
* i-prefixed methods operate on indices in parents
*/
template<typename K, typename OPS>
class mfp
{
@ -1142,13 +1147,18 @@ public:
{
}
// Finds a given element's index. If it isn't in the data structure,
// it is added as its own set
int operator()(const K &key) const
{
int i = database(key);
// If the lookup caused the database to grow,
// also add a corresponding entry in parents initialized to -1 (no parent)
parents.resize(database.size(), -1);
return i;
}
// Finds an element at given index
const K &operator[](int index) const
{
return database[index];
@ -1161,6 +1171,11 @@ public:
while (parents[p] != -1)
p = parents[p];
// p is now the representative of i
// Now we traverse from i up to the representative again
// and make p the parent of all the nodes along the way.
// This is a side effect and doesn't affect the return value.
// It speeds up future find operations
while (k != p) {
int next_k = parents[k];
parents[k] = p;
@ -1170,6 +1185,7 @@ public:
return p;
}
// Merge sets if the given indices belong to different sets
void imerge(int i, int j)
{
i = ifind(i);