package com.lxf.floyd;

import java.util.Arrays;

public class FloydAlgorithm {
    public static void main(String[] args) {
        //测试看看图是否创建成功
        char[] vertex={'A','B','C','D','E','F','G'};
        //创建邻接矩阵
        int[][] matrix=new int[vertex.length][vertex.length];
        final int  N=65535;
        matrix[0] = new int[] { 0, 5, 7, N, N, N, 2 };
        matrix[1] = new int[] { 5, 0, N, 9, N, N, 3 };
        matrix[2] = new int[] { 7, N, 0, N, 8, N, N };
        matrix[3] = new int[] { N, 9, N, 0, N, 4, N };
        matrix[4] = new int[] { N, N, 8, N, 0, 5, 4 };
        matrix[5] = new int[] { N, N, N, 4, 5, 0, 6 };
        matrix[6] = new int[] { 2, 3, N, N, 4, 6, 0 };
        Graph graph = new Graph(7, matrix, vertex);
        graph.show();
        graph.floyd();
        System.out.println();
        graph.show();
    }
}

/**
 * 创建图
 */
class Graph{
    private char[] vertex;
    private int[][]  dis;//保存，从各个顶点出发到其它顶点的距离，最后的结果，也是保留在该数组
    private int[][]  pre;//保存到达目标顶点的前驱顶点
    final int  N=65535;
    /**
     * 构造器
     * @param length  大小
     * @param matrix 邻接矩阵
     * @param vertex 顶点数组
     */
    public Graph(int length,int[][] matrix,char[] vertex) {
        this.vertex = vertex;
        this.dis=matrix;
        this.pre=new int[length][length];
        //对pre数组初始化，注意存放的是前驱顶点的下标
        for (int i = 0; i < length; i++) {
            Arrays.fill(pre[i],i);
        }
    }

    /**
     * 显示pre数组和dis数组
     */
    public void show(){
        System.out.println("前驱表：");
        for (int i = 0; i < dis.length; i++) {
            //先将pre数组输出的一行数据
            for (int j = 0; j < dis.length; j++) {
                System.out.print(pre[i][j]+" ");
            }
            System.out.println();
        }
        System.out.println();
        System.out.println("各个顶点距离表：");
        for (int i = 0; i < dis.length; i++) {
            //输出dis数组的一行数据
            for (int k = 0; k < dis.length; k++) {
                System.out.printf("%-10d ",dis[i][k]);
            }
            System.out.println();
        }
    }

    /**
     * 弗洛伊德算法
     */
    public void floyd(){
       int len=0;//变量保存距离
       //对中间顶点的遍历，k就是中间顶点的下标
        for (int i = 0; i < dis.length; i++) {
            //从i顶点开始出发：[A,B,C,D,E,F,G]
            for (int j = 0; j < dis.length; j++) {
                    if(i!=j){
                        for (int k = 0; k < dis.length; k++) {
                            if(k!=i&&k!=j&&dis[i][k]!=N&&dis[k][j]!=N){
                                len=dis[i][k]+dis[k][j];//=>求出从i顶点出发，经过k中间顶点，到达j顶点的距离
                                if(len<dis[i][j]){
                                    //如果len小于dis[i][j]
                                    dis[i][j]=len;//更新距离
                                    pre[i][j]=pre[k][j];//更新前驱顶点
                                }
                            }
                        }
                    }
                }
            }
        }
}