private int[][] directions = new int[][]{{0, 1}, {0, -1}, {1, 0}, {-1, 0}};

public int cutOffTree(List<List<Integer>> forest) {

if (forest == null || forest.size() == 0) return 0;

PriorityQueue<TreePoint> pq = new PriorityQueue<>(1, Comparator.comparingInt(p -> p.h));

int M = forest.size();

int N = forest.get(0).size();

int[][] golf = new int[M][N];

int i = 0;

for (List<Integer> level: forest) {

int j = 0;

for (Integer pos: level) {

if (pos > 1) {

pq.add(new TreePoint(i, j, pos));

}

golf[i][j] = pos;

j++;

}

i++;

}

Point pre = new Point(0, 0);

int res = 0;

while (pq.size() > 0) {

TreePoint t = pq.poll();

Point dest = new Point(t.x, t.y);

int d = minDistance(golf, pre, dest, M, N);

if (d == -1) return -1;

res += d;

golf[t.x][t.y] = 1;

pre = dest;

}

return res;

}

private int minDistance(int[][] golf, Point start, Point end, int M, int N) {

if (start.x == end.x && start.y == end.y) return 0;

Queue<Point> q = new LinkedList<>();

q.add(start);

boolean[][] visited = new boolean[M][N];

visited[start.x][start.y] = true;

int dist = 0;

while (!q.isEmpty()) {

int size = q.size();

for (int i =0; i<size; i++) {

Point curr = q.poll();

if (curr.x == end.x && curr.y == end.y) return dist;

for (int[] d: directions) {

int x = curr.x + d[0];

int y = curr.y + d[1];

if (x == end.x && y == end.y) return dist + 1;

if (x >= 0 && y >= 0 && x < M && y < N && !visited[x][y] && golf[x][y] != 0) {

q.add(new Point(x, y));

visited[x][y] = true;

}

}

}

dist++;

}

return -1;

}

class Point {

int x;

int y;

Point(int xx, int yy) {

x = xx;

y = yy;

}

}

class TreePoint {

int x;

int y;

int h;

TreePoint(int xx, int yy, int hh) {

x = xx;

y = yy;

h = hh;

}

}