在 for 循环中检索每个位置的 "n-1" 和 "n+1" 元素

Question

我有一个有向图（使用 jgrapht 库创建），它以点对象为顶点。当洪水填充算法通过给定矩阵时，我添加了顶点和边。我使用以下代码创建了它：

public static DirectedGraph<Point, DefaultEdge> directedGraph = new DefaultDirectedGraph<Point, DefaultEdge>(DefaultEdge.class);

    public static class FloodFill {


  public static void resolution(String[] args) {
    System.out.println("Found loop: "+checkIfPositionIsInLoop(matrix, 2, 7, 3));


    //result
    System.out.println("-------------------"); 

    for (int i=0; i<matrix.length; i++) {
      for (int j=0; j<matrix[i].length; j++) {
        System.out.print(matrix[i][j] + " ");
      }
      System.out.print("\n");
    }
    System.out.print("\n");
  }

  private static Direction direction;

  public static boolean checkIfPositionIsInLoop(int[][] matrix, int x, int y, int fillValue) {
    int targetX = x;
    int targetY = y;

    return fillReachesTargetPosition(matrix, x, y, targetX, targetY, fillValue, Direction.LEFT );
  }

  private static boolean fillReachesTargetPosition(int[][] matrix, int x, int y, int targetX, int targetY, int fillValue, Direction forbiddenDirection) {

    if (x>=matrix.length)
      return false;
    if (y>=matrix[x].length)
      return false;

    int originValue=matrix[x][y];
    matrix[x][y]=fillValue;

    int xToFillNext;
    int yToFillNext;

    boolean fillingReachedTargetPosition = false;

    // Up
    xToFillNext = x-1;
    yToFillNext = y;
    if (xToFillNext==targetX && yToFillNext==targetY && !forbiddenDirection.equals(Direction.UP)) {
      Point myPoint = new Point(x, y);
      Point myNextPoint = new Point(xToFillNext, yToFillNext);
      directedGraph.addVertex(myPoint);
      directedGraph.addVertex(myNextPoint);
      directedGraph.addEdge(myPoint, myNextPoint);
      //outEdgesMap.put(myPoint,outEdgesMap.get(myPoint)+1);
      return true;
    } else if (xToFillNext>=0 && originValue==matrix[xToFillNext][yToFillNext] && !forbiddenDirection.equals(Direction.UP)) {  
      Point myPoint = new Point(x, y);
      Point myNextPoint = new Point(xToFillNext, yToFillNext);
      directedGraph.addVertex(myPoint);
      directedGraph.addVertex(myNextPoint);
      directedGraph.addEdge(myPoint, myNextPoint); 
      //outEdgesMap.put(myPoint, outEdgesMap.get(myPoint)+1);  
      fillingReachedTargetPosition = 
        fillReachesTargetPosition(matrix, xToFillNext, yToFillNext, targetX, targetY, fillValue, Direction.DOWN );
      if (fillingReachedTargetPosition) {
        return true;
      }
    }

    // Right
    xToFillNext = x;
    yToFillNext = y+1;
    if (xToFillNext==targetX  && yToFillNext==targetY && !forbiddenDirection.equals(Direction.RIGHT)) {
      Point myPoint = new Point(x, y);
      Point myNextPoint = new Point(xToFillNext, yToFillNext);
      directedGraph.addVertex(myPoint);
      directedGraph.addVertex(myNextPoint);
      directedGraph.addEdge(myPoint, myNextPoint);
      //outEdgesMap.put(myPoint, outEdgesMap.get(myPoint)+1);
      return true;
    } else if (yToFillNext<matrix[xToFillNext].length && originValue==matrix[xToFillNext][yToFillNext] && !forbiddenDirection.equals(Direction.RIGHT)) {
      Point myPoint = new Point(x, y);
      Point myNextPoint = new Point(xToFillNext, yToFillNext);
      directedGraph.addVertex(myPoint);
      directedGraph.addVertex(myNextPoint);
      directedGraph.addEdge(myPoint, myNextPoint);
      //outEdgesMap.put(myPoint, outEdgesMap.get(myPoint)+1);
      fillingReachedTargetPosition = 
        fillReachesTargetPosition(matrix, xToFillNext, yToFillNext, targetX, targetY, fillValue, Direction.LEFT );
      if (fillingReachedTargetPosition) {
        return true;
      }
    }

    // Down
    xToFillNext = x+1;
    yToFillNext = y;
    if (xToFillNext==targetX && yToFillNext==targetY && !forbiddenDirection.equals(Direction.DOWN)) {
      Point myPoint = new Point(x, y);
      Point myNextPoint = new Point(xToFillNext, yToFillNext);
      directedGraph.addVertex(myPoint);
      directedGraph.addVertex(myNextPoint);
      directedGraph.addEdge(myPoint, myNextPoint);
      //outEdgesMap.put(myPoint, outEdgesMap.get(myPoint)+1);
      return true;
    } else if (xToFillNext<matrix.length  && originValue==matrix[xToFillNext][yToFillNext] && !forbiddenDirection.equals(Direction.DOWN)) {
      Point myPoint = new Point(x, y);
      Point myNextPoint = new Point(xToFillNext, yToFillNext);
      directedGraph.addVertex(myPoint);
      directedGraph.addVertex(myNextPoint);
      directedGraph.addEdge(myPoint, myNextPoint);
      //outEdgesMap.put(myPoint, outEdgesMap.get(myPoint)+1);
      fillingReachedTargetPosition = 
        fillReachesTargetPosition(matrix, xToFillNext, yToFillNext, targetX, targetY, fillValue, Direction.UP );  
      if (fillingReachedTargetPosition) {
        return true;
      }
    }

    // Left
    xToFillNext = x;
    yToFillNext = y-1;
    if (xToFillNext==targetX && yToFillNext==targetY && forbiddenDirection.equals(Direction.RIGHT)) {
      Point myPoint = new Point(x, y);
      Point myNextPoint = new Point(xToFillNext, yToFillNext);
      directedGraph.addVertex(myPoint);
      directedGraph.addVertex(myNextPoint);
      directedGraph.addEdge(myPoint, myNextPoint);
      //outEdgesMap.put(myPoint, outEdgesMap.get(myPoint)+1);
      return true;
    } else if (yToFillNext>=0 && originValue==matrix[xToFillNext][yToFillNext] && !forbiddenDirection.equals(Direction.LEFT)) {

      Point myPoint = new Point(x, y);
      Point myNextPoint = new Point(xToFillNext, yToFillNext);
      directedGraph.addVertex(myPoint);
      directedGraph.addVertex(myNextPoint);
      directedGraph.addEdge(myPoint, myNextPoint);
      //outEdgesMap.put(myPoint, outEdgesMap.get(myPoint)+1);
      fillingReachedTargetPosition = 
        fillReachesTargetPosition(matrix, xToFillNext, yToFillNext, targetX, targetY, fillValue, Direction.RIGHT );
      if (fillingReachedTargetPosition) {
        return true;
      }
    }

    return false;
  }
}

public static class Point {

  public int x;
  public int y;

  public  Point(int x, int y) 
  {

    this.x = x;
    this.y = y;
  }
  @Override
    public String toString() {
    return ("[x="+x+" y="+y+"]");
  }

  @Override
    public int hashCode() {
    int hash = 7;
    hash = 71 * hash + this.x;
    hash = 71 * hash + this.y;
    return hash;
   }



  @Override
    public boolean equals(Object other) 
  {
    if (this == other)
      return true;

    if (!(other instanceof Point))
      return false;

    Point otherPoint = (Point) other;
    return otherPoint.x == x && otherPoint.y == y;
  }
}

现在，我使用以下方式显示每个顶点的向外顶点数：

for(Point myPoint : directedGraph.vertexSet()){
   int degree = directedGraph.outDegreeOf(myPoint);
   }

我想添加一个 if 语句，其条件是向外的顶点数。例如：

for(Point myPoint : directedGraph.vertexSet()){
       int degree = directedGraph.outDegreeOf(myPoint);
if (degree >= 2 // This is the degree of the element number n){
// use n-1,n+1, n+2 etc element
}

我的问题是如何访问元素的 n-1、n+1、n+2（等）个元素？使用迭代器是否合适？

Answer 1

我使用了predecessorListOf()和successorListOf()这两个方法或多或少可以解决我的问题，因为我没有更好的选择。

在 for 循环中检索每个位置的 "n-1" 和 "n+1" 元素

Retrieve "n-1" and "n+1" element of each position in a for loop

java

algorithm

iterator

jgrapht

digraphs