[Swift]LeetCode827. 最大人工岛 | Making A Large Island

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In a 2D grid of 0s and 1s, we change at most one 0 to a 1.

After, what is the size of the largest island? (An island is a 4-directionally connected group of 1s).

Example 1:

Input: [[1, 0], [0, 1]]
Output: 3
Explanation: Change one 0 to 1 and connect two 1s, then we get an island with area = 3.

Example 2:

Input: [[1, 1], [1, 0]]
Output: 4
Explanation: Change the 0 to 1 and make the island bigger, only one island with area = 4.

Example 3:

Input: [[1, 1], [1, 1]]
Output: 4
Explanation: Can't change any 0 to 1, only one island with area = 4. 

Notes:

• 1 <= grid.length = grid[0].length <= 50.
• 0 <= grid[i][j] <= 1.

---

在二维地图上， 0代表海洋， 1代表陆地，我们最多只能将一格 0 海洋变成 1变成陆地。

进行填海之后，地图上最大的岛屿面积是多少？（上、下、左、右四个方向相连的 1 可形成岛屿）

示例 1:

输入: [[1, 0], [0, 1]]
输出: 3
解释: 将一格0变成1，最终连通两个小岛得到面积为 3 的岛屿。

示例 2:

输入: [[1, 1], [1, 0]]
输出: 4
解释: 将一格0变成1，岛屿的面积扩大为 4。

示例 3:

输入: [[1, 1], [1, 1]]
输出: 4
解释: 没有0可以让我们变成1，面积依然为 4。

说明:

• 1 <= grid.length = grid[0].length <= 50
• 0 <= grid[i][j] <= 1

---

Runtime: 104 ms

Memory Usage: 19.9 MB

class Solution {
    var N:Int = 0
    func largestIsland(_ grid: [[Int]]) -> Int {
        var grid = grid
        N = grid.count
        var index:Int = 3
        var res:Int = 0
        var area:[Int:Int] = [Int:Int]()
        for x in 0..<N
        {
            for y in 0..<N
            {
                if grid[x][y] == 1
                {
                    area[index] = dfs(&grid, x, y, index)
                    res = max(res, area[index,default:0])
                    index += 1
                }
            }
        }
        for x in 0..<N
        {
            for y in 0..<N
            {
                if grid[x][y] == 0
                {
                    var seen:Set<Int> = Set<Int>()
                    var cur:Int = 1
                    for (key,val) in move(x, y)
                    {
                        index = grid[key][val]
                        if index > 1 && !seen.contains(index)
                        {
                            seen.insert(index)
                            cur += area[index,default:0]
                        }
                    }
                    res = max(res, cur)
                }
            }
        }
        return res
    }
    
    func move(_ x:Int,_ y:Int) -> [(Int,Int)]
    {
        var res:[(Int,Int)] = [(Int,Int)]()
        if valid(x, y + 1) {res.append((x, y + 1))}
        if valid(x, y - 1) {res.append((x, y - 1))}
        if valid(x + 1, y) {res.append((x + 1, y))}
        if valid(x - 1, y) {res.append((x - 1, y))}
        return res        
    }
    
    func valid(_ x:Int,_ y:Int) -> Bool
    {
        return 0 <= x && x < N && 0 <= y && y < N
    }
    
    func dfs(_ grid:inout [[Int]],_ x:Int,_ y:Int,_ index:Int) -> Int
    {
        var area:Int = 0
        grid[x][y] = index
        for (key,val) in move(x, y)
        {
            if grid[key][val] == 1
            {
                area += dfs(&grid, key, val, index) 
            }
        }
        return area + 1
    }
}