[Swift]LeetCode317. 建築物的最短距離 $ Shortest Distance from All Buildings

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You want to build a house on an empty land which reaches all buildings in the shortest amount of distance. You can only move up, down, left and right. You are given a 2D grid of values 0, 1 or 2, where:

• Each 0 marks an empty land which you can pass by freely.
• Each 1 marks a building which you cannot pass through.
• Each 2 marks an obstacle which you cannot pass through.

For example, given three buildings at (0,0), (0,4), (2,2), and an obstacle at (0,2):

1 - 0 - 2 - 0 - 1
|   |   |   |   |
0 - 0 - 0 - 0 - 0
|   |   |   |   |
0 - 0 - 1 - 0 - 0

The point (1,2) is an ideal empty land to build a house, as the total travel distance of 3+3+1=7 is minimal. So return 7.

Note:
There will be at least one building. If it is not possible to build such house according to the above rules, return -1.

---

你想在一片空曠的土地上建造一座房子，它能在最短的距離內到達全部的建築物。你只能上下左右移動。您將獲得一個值爲0、1或2的二維網格，其中：

每0分表明一片空地，你能夠自由通行。

每1個標記一個不能穿過的建築物。

每2個標記一個你不能經過的障礙物。

例如，假設(0,0), (0,4), (2,2)處有三座建築物，而(0,2)處有障礙物：

1 - 0 - 2 - 0 - 1
|   |   |   |   |
0 - 0 - 0 - 0 - 0
|   |   |   |   |
0 - 0 - 1 - 0 - 0

因爲3+3+1=7的總行程最小，所以點(1,2)是建造房屋的理想空地。因此返回7。

注：

至少有一棟樓。若是沒法按照上述規則建造此類房屋，則返回-1。

---

Solution:

 1 class Solution {
 2     func shortestDistance(_ grid:inout [[Int]]) -> Int {
 3         var res:Int = Int.max
 4         var val:Int = 0
 5         var m:Int = grid.count
 6         var n:Int = grid[0].count
 7         var sum:[[Int]] = grid
 8         var dirs:[[Int]] = [[0,-1],[-1,0],[0,1],[1,0]]
 9         for i in 0..<grid.count
10         {
11             for j in 0..<grid[i].count
12             {
13                 if grid[i][j] == 1
14                 {
15                     res = Int.max
16                     var dist:[[Int]] = grid
17                     var q:[(Int,Int)] = [(Int,Int)]()
18                     q.append((i, j))
19                     while(!q.isEmpty)
20                     {
21                         var a:Int = q.first!.0
22                         var b:Int = q.first!.1
23                         q.removeFirst()
24                         for k in 0..<dirs.count
25                         {
26                             var x:Int = a + dirs[k][0]
27                             var y:Int = b + dirs[k][1]
28                             if x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == val
29                             {
30                                 grid[x][y] -= 1
31                                 dist[x][y] = dist[a][b] + 1
32                                 sum[x][y] += (dist[x][y] - 1)
33                                 q.append((x, y))
34                                 res = min(res, sum[x][y])
35                             }
36                         }
37                     }
38                     val -= 1
39                 }
40             }
41         }
42         return res == Int.max ? -1 : res    
43     }
44 }

點擊：Playground測試

1 var arr:[[Int]] = [[1,0,2,0,1],[0,0,0,0,0],[0,0,1,0,0]]
2 var sol = Solution()
3 print(sol.shortestDistance(&arr))
4 //Print 7