LeetCode - Cut Off Trees for Golf Event

You are asked to cut off trees in a forest for a golf event. The forest is represented as a non-negative 2D map, in this map:

0 represents the obstacle can't be reached.
1 represents the ground can be walked through.
The place with number bigger than 1 represents a tree can be walked through, and this positive number represents the tree's height.
You are asked to cut off all the trees in this forest in the order of tree's height - always cut off the tree with lowest height first. And after cutting, the original place has the tree will become a grass (value 1).

You will start from the point (0, 0) and you should output the minimum steps you need to walk to cut off all the trees. If you can't cut off all the trees, output -1 in that situation.

You are guaranteed that no two trees have the same height and there is at least one tree needs to be cut off.

Example 1:
Input: 
[
 [1,2,3],
 [0,0,4],
 [7,6,5]
]
Output: 6
Example 2:
Input: 
[
 [1,2,3],
 [0,0,0],
 [7,6,5]
]
Output: -1
Example 3:
Input: 
[
 [2,3,4],
 [0,0,5],
 [8,7,6]
]
Output: 6
Explanation: You started from the point (0,0) and you can cut off the tree in (0,0) directly without walking.
Hint: size of the given matrix will not exceed 50x50.

我用了priorityqueue+bfs 来做，但没有得到正解，目前不知道错在哪儿。。。?

class Solution {
    public int cutOffTree(List<List<Integer>> forest) {
        if(forest == null || forest.size() == 0 || forest.get(0).size() == 0 || forest.get(0).get(0) == 0){
            return -1;
        }
        int row = forest.size();
        int column = forest.get(0).size();        
        PriorityQueue<int[]> pqueue = new PriorityQueue<>((a,b) -> compare(a, b));
        int count = 0;
        for(int i = 0; i < row; i++){
            for(int j = 0; j < column; j++){
                int height = forest.get(i).get(j);
                if(height > 1 && count < 2){
                    count++;
                    Queue<int[]> queue = new LinkedList<>();
                    pqueue.add(new int[]{i,j,height});
                    queue.add(new int[]{i,j});
                    forest.get(i).set(j,1);
                    while(!queue.isEmpty()){
                        int[] temp = queue.poll();
                        int r = temp[0];
                        int c = temp[1];
                        //move up
                        if(r-1 >= 0 && forest.get(r-1).get(c) > 1){
                            queue.add(new int[]{r-1,c});
                            pqueue.add(new int[]{r-1,c,forest.get(r-1).get(c)});
                            forest.get(r-1).set(c,1);
                        }
                        //move down
                        if(r+1 < row && forest.get(r+1).get(c) > 1){
                            queue.add(new int[]{r+1,c});
                            pqueue.add(new int[]{r+1,c,forest.get(r+1).get(c)});
                            forest.get(r+1).set(c,1);
                        }                        
                        //move left
                        if(c-1 >= 0 && forest.get(r).get(c-1) > 1){
                            queue.add(new int[]{r,c-1});
                            pqueue.add(new int[]{r,c-1,forest.get(r).get(c-1) });
                            forest.get(r).set(c-1,1);                           
                        }
                        //move right
                        if(c+1 < column && forest.get(r).get(c+1) > 1){
                            queue.add(new int[]{r,c+1});
                            pqueue.add(new int[]{r,c+1,forest.get(r).get(c+1)});
                            forest.get(r).set(c+1,1);                               
                        }
                    }
                }
                else if(count >= 2){
                    return -1;
                }
            }
        }   
        int steps = 0;
        int[] start = new int[]{0,0};
        for(int[] end : pqueue){
            steps = steps + getSteps(start, end, forest, row, column);
            start = end;   
        }
        
        return steps;
    }
    
    private int getSteps(int[] start, int[] end, List<List<Integer>> forest, int row, int column){
        Queue<int[]> path = new LinkedList<>();
        int count = 0;
        boolean found = false;
        path.offer(start);
        while(!found){
            Queue<int[]> temp = new LinkedList<>();
            while(!path.isEmpty()){
                int[] point = path.poll();
                int r = point[0];
                int c = point[1];
                if(r == end[0] && c == end[1]){
                    found = true;
                    break;
                }
                //move up
                if(r - 1 >= 0 && forest.get(r-1).get(c) >= 1){
                    temp.offer(new int[]{r-1,c});
                }
                //move down
                if(r + 1 < row && forest.get(r+1).get(c) >= 1){
                    temp.offer(new int[]{r+1,c});
                }            
                //move left
                if(c - 1 >= 0 && forest.get(r).get(c-1) >= 1){
                    temp.offer(new int[]{r,c-1});
                }                
                //move right
                if(c + 1 < column && forest.get(r).get(c+1) >= 1){
                    temp.offer(new int[]{r,c+1});
                }
            }
            if(!found){
                count++;
                path = temp;
            }
        }
        return count;
    }
    private int compare(int[] a, int[] b){
        int heightA = a[2];
        int heightB = b[2];
        return heightA - heightB;
    }
}

 

转载于:https://www.cnblogs.com/incrediblechangshuo/p/9734023.html