# 迪杰斯特拉（Dijstra）算法和弗洛伊德（Floyd）算法

By [nnnnnobita](https://paragraph.com/@nnnnnobita) · 2021-12-04

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迪杰斯特拉

找到某一个顶点到其他所有顶点的最短距离

弗洛伊德

找到所有顶点之间的最短距离

    package Algorithm.floyd;
    
    import java.util.Arrays;
    
    public class floydDemo {
    
        public static void main(String[] args) {
            final int N = 65535;
            char[] vertex = {'A','B','C','D','E','F','G'};
            int[][] weight = new int[][] {
                {0,5,7,N,N,N,2},
                {5,0,N,9,N,N,3},
                {7,N,0,N,8,N,N},
                {N,9,N,0,N,4,N},
                {N,N,8,N,0,5,4},
                {N,N,N,4,5,0,6},
                {2,3,N,N,4,6,0},
                };
            Graph graph = new Graph(vertex.length, weight, vertex);
            graph.floyd();
            graph.showAll();
        }
    }
    
    class Graph{
        private char[] vertex;
        private int[][] dis;
        private int[][] pre;
        
        public Graph(int length, int[][] dis, char[] vertex) {
            this.vertex = vertex;
            this.dis = dis;
            this.pre = new int[length][length];
            for(int i=0; i<vertex.length; i++) {
                Arrays.fill(pre[i], i);   //pre[i]是第i行
            }
        }
        
        public void showAll() {
            
            for(int i=0; i<vertex.length; i++) {
                //输出pre
                for(int j=0; j<vertex.length; j++) {
                    System.out.print(pre[i][j] + " ");
                }
                System.out.println();
                //输出dis
                for(int j=0; j<vertex.length; j++) {
                    System.out.print(dis[i][j] + " ");
                }
                System.out.println();
            }
        }
        
        public void floyd() {
            int len;   // 临时变量记录经过中间节点的新的距离
            for(int k=0; k<vertex.length; k++) {   // k表示中间节点
                for(int i=0; i<vertex.length; i++) {  // i表示出发节点
                    for(int j=0; j<vertex.length; j++) {
                        len = dis[i][k] + dis[k][j];
                        if(len < dis[i][j]) {   //如果len小于两点之间的直接距离，就可以替换了
                            dis[i][j] = len;    // update the distance between i and j
                            pre[i][j] = pre[k][j];   // update the pre-vertex of i,j
                        }
                    }
                }
            }
        }
        
    }

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*Originally published on [nnnnnobita](https://paragraph.com/@nnnnnobita/dijstra-floyd)*