• ㊗️
• 大家
• offer
• 多多！

## Problem

You are given a m x n 2D grid initialized with these three possible values.

-1 - A wall or an obstacle. 0 - A gate. INF - Infinity means an empty room. We use the value 231 - 1 = 2147483647 to represent INF as you may assume that the distance to a gate is less than 2147483647. Fill each empty room with the distance to its nearest gate. If it is impossible to reach a gate, it should be filled with INF.

Example:

Given the 2D grid:

INF  -1  0  INF
INF INF INF  -1
INF  -1 INF  -1
0  -1 INF INF


After running your function, the 2D grid should be:

  3  -1   0   1
2   2   1  -1
1  -1   2  -1
0  -1   3   4


## Code

class Solution {
public void wallsAndGates(int[][] rooms) {

for(int i = 0; i < rooms.length; i++){
for(int j = 0; j < rooms[0].length; j++){
if(rooms[i][j] == 0){
}
}
}

int[][] dirs = {{-1, 0}, {1, 0}, {0, 1}, {0, -1}};

int curr = 0;
while(!queue.isEmpty()){
int size = queue.size();
for(int i = 0; i < size; i++){
int[] loc = queue.poll();
int row = loc[0];
int col = loc[1];
rooms[row][col] = Math.min(curr, rooms[row][col]);

for(int[] dir : dirs){
int x = row + dir[0];
int y = col + dir[1];

if(x < 0 || y < 0 || x >= rooms.length || y >= rooms[0].length) continue;
if(rooms[x][y] != Integer.MAX_VALUE) continue;

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

curr++;
}
}
}

class Solution:
def helper(self, i: int, j: int, step: int, rooms: List[List[int]]) -> None:
if i < 0 or i >= len(rooms) or j < 0 or j >= len(rooms[0]):
return

if rooms[i][j] < step:
return

rooms[i][j] = step

self.helper(i + 1, j, step + 1, rooms)
self.helper(i - 1, j, step + 1, rooms)
self.helper(i, j + 1, step + 1, rooms)
self.helper(i, j - 1, step + 1, rooms)

def wallsAndGates(self, rooms: List[List[int]]) -> None:
"""
Do not return anything, modify rooms in-place instead.
"""
for i in range(len(rooms)):
for j in range(len(rooms[0])):
if rooms[i][j] == 0:
self.helper(i, j, 0, rooms)

class Solution:
def wallsAndGates(self, rooms: List[List[int]]) -> None:
"""
Do not return anything, modify rooms in-place instead.
"""
queue = deque()

for i in range(len(rooms)):
for j in range(len(rooms[0])):
if rooms[i][j] == 0:
queue.append((i, j))
step = 0
moves = [[1, 0], [-1, 0], [0, 1], [0, -1]]
while len(queue):
size = len(queue)
for i in range(size):
node = queue.popleft()
for move_index in range(4):
move = moves[move_index]
next_i = node[0] + move[0]
next_j = node[1] + move[1]
if next_i < 0 or next_i >= len(rooms) or next_j < 0 or next_j >= len(rooms[0]):
continue

if rooms[next_i][next_j] < step + 1:
continue

rooms[next_i][next_j] = step + 1
queue.append((next_i, next_j))

step += 1