[Swift]LeetCode1036.逃离大迷宫 | Escape a Large Maze

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In a 1 million by 1 million grid, the coordinates of each grid square are (x, y) with 0 <= x, y < 10^6.

We start at the source square and want to reach the target square.  Each move, we can walk to a 4-directionally adjacent square in the grid that isn't in the given list of blocked squares.

Return true if and only if it is possible to reach the target square through a sequence of moves.

Example 1:

Input: blocked = [[0,1],[1,0]], source = [0,0], target = [0,2]
Output: false
Explanation: 
The target square is inaccessible starting from the source square, because we can't walk outside the grid.

Example 2:

Input: blocked = [], source = [0,0], target = [999999,999999]
Output: true
Explanation: 
Because there are no blocked cells, it's possible to reach the target square.

Note:

1. 0 <= blocked.length <= 200
2. blocked[i].length == 2
3. 0 <= blocked[i][j] < 10^6
4. source.length == target.length == 2
5. 0 <= source[i][j], target[i][j] < 10^6
6. source != target

---

在一个 10^6 x 10^6 的网格中，每个网格块的坐标为 (x, y)，其中 0 <= x, y < 10^6。

我们从源方格 source 开始出发，意图赶往目标方格 target。每次移动，我们都可以走到网格中在四个方向上相邻的方格，只要该方格不在给出的封锁列表 blocked 上。

只有在可以通过一系列的移动到达目标方格时才返回 true。否则，返回 false。

示例 1：

输入：blocked = [[0,1],[1,0]], source = [0,0], target = [0,2]
输出：false
解释：
从源方格无法到达目标方格，因为我们无法在网格中移动。

示例 2：

输入：blocked = [], source = [0,0], target = [999999,999999]
输出：true
解释：
因为没有方格被封锁，所以一定可以到达目标方格。

提示：

1. 0 <= blocked.length <= 200
2. blocked[i].length == 2
3. 0 <= blocked[i][j] < 10^6
4. source.length == target.length == 2
5. 0 <= source[i][j], target[i][j] < 10^6
6. source != target

---

Runtime: 3096 ms

Memory Usage: 24.7 MB

class Solution {
    func isEscapePossible(_ blocked: [[Int]], _ source: [Int], _ target: [Int]) -> Bool {
        var set:Set<Int> = Set<Int>()
        for b in blocked
        {
            set.insert(b[0]<<32|b[1])
            if set.contains(source[0]<<32|source[1]) {return false}
            if set.contains(target[0]<<32|target[1]) {return false}
        }
        
        var ss:[[Bool]] = go(source[0], source[1], set)
        var ts:[[Bool]] = go(target[0], target[1], set)
        if abs(source[0] - target[0]) > 200 || abs(source[1] - target[1]) > 200
        {
            var pt:Int  = 0
            for i in 0..<411
            {
                for j in 0..<411
                {
                    if i == 0 || j == 0 || i == 410 || j == 410
                    {
                        if ss[i][j] {pt |= 1}
                        if ts[i][j] {pt |= 2}
                    }
                }
            }
            return pt == 3
        }
        else
        {
            return ss[target[0]-source[0]+205][target[1]-source[1]+205]
        }
    }
    
    func go(_ sr:Int,_ sc:Int,_ obs:Set<Int>) -> [[Bool]]
    {
        var can:[[Bool]] = [[Bool]](repeating: [Bool](repeating: false, count: 411), count: 411)
        can[205][205] = true
        var q:[[Int]] = [[Int]]()
        q.append([205, 205])
        let dr:[Int] = [ 1, 0, -1, 0 ]
        let dc:[Int] = [ 0, 1, 0, -1 ]
        while(!q.isEmpty)
        {
            var cur:[Int] = q.removeLast()
            let r:Int = cur[0]
            let c:Int = cur[1]
            for k in 0..<4
            {
                let nr:Int = r + dr[k]
                let nc:Int = c + dc[k]
                if nr >= 0 && nr < 411 && nc >= 0 && nc < 411 && !can[nr][nc]
                    && sr-205+nr >= 0 && sr-205+nr < 1000000
                    && sc-205+nc >= 0 && sc-205+nc < 1000000
                    && !obs.contains((sr-205+nr)<<32|(sc-205+nc))
                {
                    can[nr][nc] = true
                    q.append([nr, nc])
                }
            }
        }
        return can
    }
}