Disjoint Set Union with Rollback
(data-structure/dsu_rollback.hpp)

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• Last update: 2023-07-25 00:50:50+07:00
• Include: #include "data-structure/dsu_rollback.hpp"

Code

#pragma once

struct dsu_rollback {
  vector<int> data;
  stack<pair<int, int>> history;
  int inner_snap;

  dsu_rollback(int sz) : inner_snap(0) { data.assign(sz, -1); }

  bool merge(int x, int y) {
    x = root(x), y = root(y);
    history.emplace(x, data[x]);
    history.emplace(y, data[y]);
    if (x == y) return false;
    if (data[x] > data[y]) swap(x, y);
    data[x] += data[y];
    data[y] = x;
    return true;
  }

  int root(int k) {
    if (data[k] < 0) return k;
    return root(data[k]);
  }

  int same(int x, int y) { return root(x) == root(y); }

  int size(int k) { return (-data[root(k)]); }

  void undo() {
    data[history.top().first] = history.top().second;
    history.pop();
    data[history.top().first] = history.top().second;
    history.pop();
  }

  void snapshot() { inner_snap = int(history.size() >> 1); }

  int get_state() { return int(history.size() >> 1); }

  void rollback(int state = -1) {
    if (state == -1) state = inner_snap;
    state <<= 1;
    assert(state <= (int)history.size());
    while (state < (int)history.size()) undo();
  }
};

#line 2 "data-structure/dsu_rollback.hpp"

struct dsu_rollback {
  vector<int> data;
  stack<pair<int, int>> history;
  int inner_snap;

  dsu_rollback(int sz) : inner_snap(0) { data.assign(sz, -1); }

  bool merge(int x, int y) {
    x = root(x), y = root(y);
    history.emplace(x, data[x]);
    history.emplace(y, data[y]);
    if (x == y) return false;
    if (data[x] > data[y]) swap(x, y);
    data[x] += data[y];
    data[y] = x;
    return true;
  }

  int root(int k) {
    if (data[k] < 0) return k;
    return root(data[k]);
  }

  int same(int x, int y) { return root(x) == root(y); }

  int size(int k) { return (-data[root(k)]); }

  void undo() {
    data[history.top().first] = history.top().second;
    history.pop();
    data[history.top().first] = history.top().second;
    history.pop();
  }

  void snapshot() { inner_snap = int(history.size() >> 1); }

  int get_state() { return int(history.size() >> 1); }

  void rollback(int state = -1) {
    if (state == -1) state = inner_snap;
    state <<= 1;
    assert(state <= (int)history.size());
    while (state < (int)history.size()) undo();
  }
};

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