Java学习笔记（day37）

一、学习内容

主题：十字链表

定义：十字链表(Orthogonal List)是有向图的另一种链式存储结构。该结构可以看成是将有向图的邻接表和逆邻接表结合起来得到的。

十字链表示意图

使用十字链表压缩存储稀疏矩阵时，矩阵中的各行各列都各用一各链表存储，与此同时，所有行链表的表头存储到一个数组（rhead），所有列链表的表头存储到另一个数组（chead）中。

二、代码编写

package datastructure.graph;

/**
 * Orthogonal List for directed graph.
 * 
 * @author Wei Ze [email protected].
 */
public class OrthogonalList {

	/**
	 * An inner class for adjacent node.
	 */
	class OrthogonalNode {
		/**
		 * The row index.
		 */
		int row;

		/**
		 * The column index.
		 */
		int column;

		/**
		 * The next out node.
		 */
		OrthogonalNode nextOut;

		/**
		 * The next in node.
		 */
		OrthogonalNode nextIn;

		/**
		 *********************
		 * The first constructor.
		 * 
		 * @param paraRow    The row.
		 * @param paraColumn The column.
		 *********************
		 */
		public OrthogonalNode(int paraRow, int paraColumn) {
			row = paraRow;
			column = paraColumn;
			nextOut = null;
			nextIn = null;
		}// Of OrthogonalNode
	}// Of class OrthogonalNode

	/**
	 * The number of nodes. This member variable may be redundant since it is always
	 * equal to headers.length.
	 */
	int numNodes;

	/**
	 * The headers for each row.
	 */
	OrthogonalNode[] headers;

	/**
	 *********************
	 * The first constructor.
	 * 
	 * @param paraMatrix The matrix indicating the graph.
	 *********************
	 */
	public OrthogonalList(int[][] paraMatrix) {
		numNodes = paraMatrix.length;

		// Step 1. Initialize. The data in the headers are not meaningful.
		OrthogonalNode tempPreviousNode, tempNode;

		headers = new OrthogonalNode[numNodes];

		// Step 2. Link to its out nodes.
		for (int i = 0; i < numNodes; i++) {
			headers[i] = new OrthogonalNode(i, -1);
			tempPreviousNode = headers[i];
			for (int j = 0; j < numNodes; j++) {
				if (paraMatrix[i][j] == 0) {
					continue;
				} // Of if

				// Create a new node.
				tempNode = new OrthogonalNode(i, j);

				// Link.
				tempPreviousNode.nextOut = tempNode;
				tempPreviousNode = tempNode;
			} // Of for j
		} // Of for i

		// Step 3. Link to its in nodes. This step is harder.
		OrthogonalNode[] tempColumnNodes = new OrthogonalNode[numNodes];
		for (int i = 0; i < numNodes; i++) {
			tempColumnNodes[i] = headers[i];
		} // Of for i

		for (int i = 0; i < numNodes; i++) {
			tempNode = headers[i].nextOut;
			while (tempNode != null) {
				tempColumnNodes[tempNode.column].nextIn = tempNode;
				tempColumnNodes[tempNode.column] = tempNode;

				tempNode = tempNode.nextOut;
			} // Of while
		} // Of for i
	}// Of the constructor

	/**
	 *********************
	 * Overrides the method claimed in Object, the superclass of any class.
	 *********************
	 */
	public String toString() {
		String resultString = "Out arcs: ";

		OrthogonalNode tempNode;
		for (int i = 0; i < numNodes; i++) {
			tempNode = headers[i].nextOut;

			while (tempNode != null) {
				resultString += " (" + tempNode.row + ", " + tempNode.column + ")";
				tempNode = tempNode.nextOut;
			} // Of while
			resultString += "\r\n";
		} // Of for i

		resultString += "\r\nIn arcs: ";

		for (int i = 0; i < numNodes; i++) {
			tempNode = headers[i].nextIn;

			while (tempNode != null) {
				resultString += " (" + tempNode.row + ", " + tempNode.column + ")";
				tempNode = tempNode.nextIn;
			} // Of while
			resultString += "\r\n";
		} // Of for i

		return resultString;
	}// Of toString

	/**
	 *********************
	 * The entrance of the program.
	 * 
	 * @param args Not used now.
	 *********************
	 */
	public static void main(String args[]) {
		int[][] tempMatrix = { { 0, 1, 0, 0 }, { 0, 0, 0, 1 }, { 1, 0, 0, 0 }, { 0, 1, 1, 0 } };
		OrthogonalList tempList = new OrthogonalList(tempMatrix);
		System.out.println("The data are:\r\n" + tempList);
	}// Of main
}// Of class OrthogonalList

三、总结

用十字链表来存储有向图，可以达到高效的存取效果。同时，代码的可读性也会得到提升。