spreadsheet.mapper.w2o.validation.engine.DependencyCycleCheckEngine Maven / Gradle / Ivy

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package spreadsheet.mapper.w2o.validation.engine;

import org.apache.commons.lang3.StringUtils;

import java.util.*;

/**
 *  * use Tarjan's strongly connected components algorithm to check cycling,
 * in directed graph, if a strongly connected component not a isolated node, means has cycle.
 * 
 * Created by hanwen on 2017/1/5.
 */
public class DependencyCycleCheckEngine {

  private LinkedHashMap> vGraph = new LinkedHashMap<>();
  private Stack vStack = new Stack<>();
  private Map vIndex = new HashMap<>();
  private Map vLowLink = new HashMap<>();
  private int index;

  // found exists cycle
  private List cycle = new ArrayList<>();

  public DependencyCycleCheckEngine(LinkedHashMap> vGraph) {
    this.vGraph = vGraph;
    for (String s : vGraph.keySet()) {
      vIndex.put(s, 0);
      vLowLink.put(s, 0);
    }
  }

  public boolean cycling() {
    for (String v : vGraph.keySet()) {

      if (vGraph.get(v).contains(v)) {
        cycle = Collections.singletonList(v);
      }

      if (isCycling()) {
        return true;
      }

      if (vIndex.get(v) == 0) {
        strongConnect(v);
      }
    }

    return false;
  }

  public List getCycle() {
    return cycle;
  }

  private void strongConnect(String v) {
    index++;
    vIndex.put(v, index);
    vLowLink.put(v, index);
    vStack.push(v);

    for (String w : vGraph.get(v)) {

      if (vIndex.get(w) == 0) {
        strongConnect(w);
        vLowLink.put(v, Math.min(vLowLink.get(v), vLowLink.get(w)));
      } else if (vStack.contains(w)) {
        vLowLink.put(v, Math.min(vLowLink.get(v), vIndex.get(w)));
      }
    }

    if (isCycling()) {
      return;
    }

    if (Objects.equals(vLowLink.get(v), vIndex.get(v))) {
      populateConnectedComponents(v);
    }
  }

  private void populateConnectedComponents(String v) {
    List connectedComponents = new ArrayList<>();
    String connectedComponent = null;

    while (!StringUtils.equals(connectedComponent, v)) {
      connectedComponent = vStack.pop();
      connectedComponents.add(connectedComponent);
    }

    if (connectedComponents.size() > 1) {
      cycle = connectedComponents;
    }
  }

  private boolean isCycling() {
    return !cycle.isEmpty();
  }
}