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// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Copyright 2005-2010 Google, Inc.
// Author: wojciech@google.com (Wojciech Skut)
//
// \file Union-Find algorithm for dense sets of non-negative
// integers. Implemented using disjoint tree forests with rank
// heuristics and path compression.
#ifndef __fst_union_find_inl_h__
#define __fst_union_find_inl_h__
#include <stack>
#include <vector>
using std::vector;
#include <fst/types.h>
namespace fst {
// Union-Find algorithm for dense sets of non-negative integers
// (exact type: T).
template <class T>
class UnionFind {
public:
// Ctor: creates a disjoint set forest for the range [0;max).
// 'fail' is a value indicating that an element hasn't been
// initialized using MakeSet(...). The upper bound of the range
// can be reset (increased) using MakeSet(...).
UnionFind(T max, T fail)
: parent_(max, fail), rank_(max), fail_(fail) { }
// Finds the representative of the set 'item' belongs to.
// Performs path compression if needed.
T FindSet(T item) {
if (item >= parent_.size()
|| item == fail_
|| parent_[item] == fail_) return fail_;
T *p = &parent_[item];
for (; *p != item; item = *p, p = &parent_[item]) {
exec_stack_.push(p);
}
for (; ! exec_stack_.empty(); exec_stack_.pop()) {
*exec_stack_.top() = *p;
}
return *p;
}
// Creates the (destructive) union of the sets x and y belong to.
void Union(T x, T y) {
Link(FindSet(x), FindSet(y));
}
// Initialization of an element: creates a singleton set containing
// 'item'. The range [0;max) is reset if item >= max.
T MakeSet(T item) {
if (item >= parent_.size()) {
// New value in parent_ should be initialized to fail_
size_t nitem = item > 0 ? 2 * item : 2;
parent_.resize(nitem, fail_);
rank_.resize(nitem);
}
parent_[item] = item;
return item;
}
// Initialization of all elements starting from 0 to max - 1 to distinct sets
void MakeAllSet(T max) {
parent_.resize(max);
for (T item = 0; item < max; ++item) {
parent_[item] = item;
}
}
private:
vector<T> parent_; // Parent nodes.
vector<int> rank_; // Rank of an element = min. depth in tree.
T fail_; // Value indicating lookup failure.
stack<T*> exec_stack_; // Used for path compression.
// Links trees rooted in 'x' and 'y'.
void Link(T x, T y) {
if (x == y) return;
if (rank_[x] > rank_[y]) {
parent_[y] = x;
} else {
parent_[x] = y;
if (rank_[x] == rank_[y]) {
++rank_[y];
}
}
}
DISALLOW_COPY_AND_ASSIGN(UnionFind);
};
} // namespace fst
#endif // __fst_union_find_inl_h__
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