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#include "graph/shortest-path/k-shortest-walk.hpp"
頂点 $s$ から $t$ へのウォーク(Walk) のうち, 昇順 $k$ 個のウォークの長さを Eppstein’s Algorithm により求める.
ウォーク(Walk, 歩道, 経路) とは重複して頂点や辺が現れることを許容した頂点 $s$ から $t$ への経路を指す.
ちなみにトレイル(Trail) は同じ辺を通らない経路, 道(Path) は同じ頂点を通らない経路である.
k_shotest_walk(g, s, t, k)
: 重み付き有向グラフ g
の頂点 s
から t
へのウォークのうち, 昇順 k
個のウォークの長さを返す(ウォークの個数が k
個に満たないとき全てを返す).#pragma once
#include "../graph-template.hpp"
/**
* @brief K-Shortest-Walk
*
* @see https://qiita.com/hotman78/items/42534a01c4bd05ed5e1e
*/
template <typename T>
vector<T> k_shortest_walk(const Graph<T> &g, int s, int t, int k) {
int N = (int)g.size();
Graph<T> rg(N);
for (int i = 0; i < N; i++) {
for (auto &e : g[i]) rg.add_directed_edge(e.to, i, e.cost);
}
auto dist = dijkstra(rg, t);
if (dist.from[s] == -1) return {};
auto &p = dist.dist;
vector<vector<int> > ch(N);
for (int i = 0; i < N; i++) {
if (dist.from[i] >= 0) ch[dist.from[i]].emplace_back(i);
}
using PHeap = PersistentLeftistHeap<T>;
using Node = typename PHeap::Node;
PHeap heap;
vector<Node *> h(N, heap.make_root());
{
queue<int> que;
que.emplace(t);
while (!que.empty()) {
int idx = que.front();
que.pop();
if (dist.from[idx] >= 0) {
h[idx] = heap.meld(h[idx], h[dist.from[idx]]);
}
bool used = true;
for (auto &e : g[idx]) {
if (e.to != t && dist.from[e.to] == -1) continue;
if (used && dist.from[idx] == e.to && p[e.to] + e.cost == p[idx]) {
used = false;
continue;
}
h[idx] = heap.push(h[idx], e.cost - p[idx] + p[e.to], e.to);
}
for (auto &to : ch[idx]) que.emplace(to);
}
}
using pi = pair<T, Node *>;
auto comp = [](const pi &x, const pi &y) { return x.first > y.first; };
priority_queue<pi, vector<pi>, decltype(comp)> que(comp);
Node *root = heap.make_root();
root = heap.push(root, p[s], s);
que.emplace(p[s], root);
vector<T> ans;
while (!que.empty()) {
T cost;
Node *cur;
tie(cost, cur) = que.top();
que.pop();
ans.emplace_back(cost);
if ((int)ans.size() == k) break;
if (cur->l) que.emplace(cost + cur->l->key - cur->key, cur->l);
if (cur->r) que.emplace(cost + cur->r->key - cur->key, cur->r);
if (h[cur->idx]) que.emplace(cost + h[cur->idx]->key, h[cur->idx]);
}
return ans;
}
#line 2 "graph/shortest-path/k-shortest-walk.hpp"
#line 2 "graph/graph-template.hpp"
/**
* @brief Graph Template(グラフテンプレート)
*/
template <typename T = int>
struct Edge {
int from, to;
T cost;
int idx;
Edge() = default;
Edge(int from, int to, T cost = 1, int idx = -1)
: from(from), to(to), cost(cost), idx(idx) {}
operator int() const { return to; }
};
template <typename T = int>
struct Graph {
vector<vector<Edge<T> > > g;
int es;
Graph() = default;
explicit Graph(int n) : g(n), es(0) {}
size_t size() const { return g.size(); }
void add_directed_edge(int from, int to, T cost = 1) {
g[from].emplace_back(from, to, cost, es++);
}
void add_edge(int from, int to, T cost = 1) {
g[from].emplace_back(from, to, cost, es);
g[to].emplace_back(to, from, cost, es++);
}
void read(int M, int padding = -1, bool weighted = false,
bool directed = false) {
for (int i = 0; i < M; i++) {
int a, b;
cin >> a >> b;
a += padding;
b += padding;
T c = T(1);
if (weighted) cin >> c;
if (directed)
add_directed_edge(a, b, c);
else
add_edge(a, b, c);
}
}
inline vector<Edge<T> > &operator[](const int &k) { return g[k]; }
inline const vector<Edge<T> > &operator[](const int &k) const { return g[k]; }
};
template <typename T = int>
using Edges = vector<Edge<T> >;
#line 4 "graph/shortest-path/k-shortest-walk.hpp"
/**
* @brief K-Shortest-Walk
*
* @see https://qiita.com/hotman78/items/42534a01c4bd05ed5e1e
*/
template <typename T>
vector<T> k_shortest_walk(const Graph<T> &g, int s, int t, int k) {
int N = (int)g.size();
Graph<T> rg(N);
for (int i = 0; i < N; i++) {
for (auto &e : g[i]) rg.add_directed_edge(e.to, i, e.cost);
}
auto dist = dijkstra(rg, t);
if (dist.from[s] == -1) return {};
auto &p = dist.dist;
vector<vector<int> > ch(N);
for (int i = 0; i < N; i++) {
if (dist.from[i] >= 0) ch[dist.from[i]].emplace_back(i);
}
using PHeap = PersistentLeftistHeap<T>;
using Node = typename PHeap::Node;
PHeap heap;
vector<Node *> h(N, heap.make_root());
{
queue<int> que;
que.emplace(t);
while (!que.empty()) {
int idx = que.front();
que.pop();
if (dist.from[idx] >= 0) {
h[idx] = heap.meld(h[idx], h[dist.from[idx]]);
}
bool used = true;
for (auto &e : g[idx]) {
if (e.to != t && dist.from[e.to] == -1) continue;
if (used && dist.from[idx] == e.to && p[e.to] + e.cost == p[idx]) {
used = false;
continue;
}
h[idx] = heap.push(h[idx], e.cost - p[idx] + p[e.to], e.to);
}
for (auto &to : ch[idx]) que.emplace(to);
}
}
using pi = pair<T, Node *>;
auto comp = [](const pi &x, const pi &y) { return x.first > y.first; };
priority_queue<pi, vector<pi>, decltype(comp)> que(comp);
Node *root = heap.make_root();
root = heap.push(root, p[s], s);
que.emplace(p[s], root);
vector<T> ans;
while (!que.empty()) {
T cost;
Node *cur;
tie(cost, cur) = que.top();
que.pop();
ans.emplace_back(cost);
if ((int)ans.size() == k) break;
if (cur->l) que.emplace(cost + cur->l->key - cur->key, cur->l);
if (cur->r) que.emplace(cost + cur->r->key - cur->key, cur->r);
if (h[cur->idx]) que.emplace(cost + h[cur->idx]->key, h[cur->idx]);
}
return ans;
}