Dijkstra算法求最短路徑

public class Dijk {


    public static void dijkstra(int v,int[][] f,int[] d,int[] pre) {
        int n = d.length-1;
        boolean[] s = new boolean[n+1];
        for(int j=1;j<=n;j++) {
            d[j] = f[v][j];
            s[j] = false;
            if(d[j] == Integer.MAX_VALUE)
                pre[j] = 0;
            else
                pre[j] = v;
        }
        s[v] = true;
        d[v] = 0;
        int u = v;
        int min;
        for(int i=1;i<n;i++) {
            min = Integer.MAX_VALUE;
            for(int j=1;j<=n;j++) {
                if((!s[j])&&min > d[j]) {
                    min = d[j];
                    u = j;
                }
            }
            s[u] = true;
            for(int j=1;j<=n;j++) {
                if ((!s[j]) && (f[u][j] < Integer.MAX_VALUE)) {
                    int newdist = d[u] + f[u][j];
                    if (newdist < d[j]) {
                        d[j] = newdist;
                        pre[j] = u;
                    }
                }
            }
        }
    }

    public static void trace(int[] pres, int pre) {
        if(pre ==1) {
            System.out.print(1);
            return;
        }
        if(pre ==0){
            System.out.println("不可達");
            return;
        }
        trace(pres,pres[pre]);
        System.out.print(" " + pre);
    }
    public static void main(String[] args) {
        int max = Integer.MAX_VALUE;
        //有線圖各頂點之間的距離權重，max爲不可達
        int[][] a = {
                { max, max, max, max, max, max, max},
                { max, 0  , 3  , 4  , max, max, max},
                { max, max, 0  , 1  , 9  , 4  , max},
                { max, max, max, 0  , 5  , 13 , max},
                { max, max, max, max,0   , max, 8  },
                { max, max, max, max, 12 , 0  , 10 },
                { max, max, max, max, max, max, 0  }
        };
        int n = a.length;
        //最短距離
        int[] dist = new int[n];
        //距離上個頂點
        int[] prev = new int[n];
        dijkstra(1, a, dist, prev);
        System.out.print(" 頂點1到2的最短路徑： ");
        trace(prev, 2);
        System.out.println();
        System.out.print(" 頂點1到3的最短路徑： ");
        trace(prev, 3);
        System.out.println();
        System.out.print(" 頂點1到4的最短路徑： ");
        trace(prev, 4);
        System.out.println();
        System.out.print(" 頂點1到5的最短路徑： ");
        trace(prev, 5);
        System.out.println();
        System.out.print(" 頂點1到6的最短路徑： ");
        trace(prev, 6);
    }
}