[675. 为高尔夫比赛砍树] dijkstra算法

import java.util.*;

class Solution {
    public int cutOffTree(List<List<Integer>> forest) {
        int m = forest.size();
        int n = forest.get(0).size();

        int[][][][] f = new int[m][n][m][n];

        int max = m * n;
        init(forest, m, n, f);

//        floyd(forest, n, f, max);

        List<int[]> list = new ArrayList<>();
        list.add(new int[]{0,0,0});
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                int val = forest.get(i).get(j);
                if( val > 1){
                    list.add(new int[]{i,j,val});
                }
            }
        }
        Collections.sort(list, new Comparator<int[]>() {
            @Override
            public int compare(int[] o1, int[] o2) {
                return o1[2] - o2[2];
            }
        });

        int ans = 0;
        for(int i=0;i<list.size()-1;i++){
            int[] val = list.get(i);
            int x = val[0];
            int y = val[1];
            int[] nextVal = list.get(i+1);
            int tmp =  dijkstra(forest,x,y,f,nextVal[0],nextVal[1]);
            if(tmp == -1){
                return -1;
            }
            ans += tmp;
        }

        return ans;
    }

    public int dijkstra(List<List<Integer>> forest,int x,int y ,int[][][][] f,int nextx,int nexty){
        PriorityQueue<int[]> queue = new PriorityQueue<>(new Comparator<int[]>() {
            @Override
            public int compare(int[] o1, int[] o2) {
                return o1[2] - o2[2];
            }
        });

        queue.offer(new int[]{x,y,0});

        int m = forest.size();
        int n = forest.get(0).size();
        boolean[][] visited = new boolean[m][n];
        visited[x][y] = true;

        while( !queue.isEmpty()) {
            int[] node = queue.poll();
            if( node[2] == Integer.MAX_VALUE){
                continue;
            }
            if(node[0] == nextx &&node[1] == nexty){
                return f[x][y][nextx][nexty];
            }
            int[][] dirs = new int[][]{
                    {0, 1}, {0, -1},
                    {-1, 0}, {1,0}
            };
            for (int i = 0; i < 4; i++) {
                int newx = node[0] + dirs[i][0];
                int newy = node[1] + dirs[i][1];

                if (newx >= 0 && newx < m && newy >= 0 && newy < n && !visited[newx][newy] && forest.get(newx).get(newy)!=0) {
                    visited[newx][newy] = true;
                    int xk = node[0];
                    int yk = node[1];
                    f[x][y][newx][newy] = f[x][y][xk][yk]+1;
                    queue.add(new int[]{newx,newy,f[x][y][newx][newy]});
                }
            }
        }
        return -1;
    }

    private void floyd(List<List<Integer>> forest, int n, int[][][][] f, int max) {
        for (int k = 0; k < max; k++) {
            int val = forest.get(k/ n).get(k% n);
            if( val == 0){
                continue;
            }
            for (int i = 0; i < max; i++) {
                if (f[i / n][i % n][k / n][k % n] == Integer.MAX_VALUE) {
                    continue;
                }
                val = forest.get(i/ n).get(i% n);
                if( val == 0){
                    continue;
                }
                for (int j = 0; j < max; j++) {
                    if (f[k / n][k % n][j / n][j % n] == Integer.MAX_VALUE) {
                        continue;
                    }
                    f[i / n][i % n][j / n][j % n] = Math.min(f[i / n][i % n][j / n][j % n], f[i / n][i % n][k / n][k % n] + f[k / n][k % n][j / n][j % n]);
                }
            }
        }
    }

    private void init(List<List<Integer>> forest, int m, int n, int[][][][] f) {
        int[][] dirs = new int[][]{
                {0, 1}, {0, -1},
                {-1, 0}, {1,0}
        };
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                for (int ii = 0; ii < m; ii++) {
                    for (int jj = 0; jj < n; jj++) {
                        f[i][j][ii][jj] = Integer.MAX_VALUE;
                        if (i == ii && jj == j) {
                            f[i][j][i][j] = 0;
                        }
                    }
                }

            }
        }

        for (int x = 0; x < m; x++) {
            for (int y = 0; y < n; y++) {
                for (int d = 0; d < 4; d++) {
                    int newx = x + dirs[d][0];
                    int newy = y + dirs[d][1];

                    if (newx >= 0 && newx < m && newy >= 0 && newy < n) {
                        int v1 = forest.get(x).get(y);
                        int v2 = forest.get(newx).get(newy);

                        if (v1 == 0 || v2 == 0) {
                            f[x][y][newx][newy] = Integer.MAX_VALUE;
                            f[newx][newy][x][y] = Integer.MAX_VALUE;
                        } else {
                                f[x][y][newx][newy] = 1;
                                f[newx][newy][x][y] = 1;
                            }
                        }
                }
            }
        }
    }

}