Dijkstra算法 Java实现

Posted 2020-09-13 Truth & Free

 

public class Dijkstra {

	private static int N = 1000;
	private static int[][] Graph = { 
			{ 0, 1, 5, N, N, N, N, N, N }, 
			{ 1, 0, 3, 7, 5, N, N, N, N },
			{ 5, 3, 0, N, 1, 7, N, N, N }, 
			{ N, 7, N, 0, 2, N, 3, N, N }, 
			{ N, 5, 1, 2, 0, 3, 6, 9, N },
			{ N, N, 7, N, 3, 0, N, 5, N }, 
			{ N, N, N, 3, 6, N, 0, 2, 7 }, 
			{ N, N, N, N, 9, 5, 2, 0, 4 },
			{ N, N, N, N, N, N, 7, 4, 0 } };

	public static void main(String[] args) {
		dijkstra(0, Graph);
	}

	/**
	 * Dijkstra最短路径。
	 * 即图中"节点vs"到其它各个节点的最短路径。
	 * @param vs 起始节点
	 * @param Graph 图
	 */
	public static void dijkstra(int vs, int[][] Graph) {
		int NUM = Graph[0].length;
		// 前驱节点数组
		int[] prenode = new int[NUM];
		// 最短距离数组
		int[] mindist = new int[NUM];
		// 该节点是否已经找到最短路径
		boolean[] find = new boolean[NUM];
		
		int vnear = 0;
		
		for (int i = 0; i < mindist.length; i++) {
			prenode[i] = i;
			mindist[i] = Graph[vs][i];
			find[i] = false;
		}

		find[vs] = true;

		for (int v = 1; v < Graph.length; v++) {

			// 每次循环求得距离vs最近的节点vnear和最短距离min
			int min = N;
			for (int j = 0; j < Graph.length; j++) {
				if (!find[j] && mindist[j] < min) {
					min = mindist[j];
					vnear = j;
				}
			}
			find[vnear] = true;

			// 根据vnear修正vs到其他所有节点的前驱节点及距离
			for (int k = 0; k < Graph.length; k++) {
				if (!find[k] && (min + Graph[vnear][k]) < mindist[k]) {
					prenode[k] = vnear;
					mindist[k] = min + Graph[vnear][k];
				}
			}
		}
		
		for (int i = 0; i < NUM; i++) {
			System.out.println("v" + vs + "...v" + prenode[i] + "->v" + i + ", s=" + mindist[i]);
		}
	}