leetcode-1254

/**
<p>二维矩阵 <code>grid</code>&nbsp;由 <code>0</code>&nbsp;（土地）和 <code>1</code>&nbsp;（水）组成。岛是由最大的4个方向连通的 <code>0</code>&nbsp;组成的群，封闭岛是一个&nbsp;<code>完全</code> 由1包围（左、上、右、下）的岛。</p>

<p>请返回 <em>封闭岛屿</em> 的数目。</p>

<p>&nbsp;</p>

<p><strong>示例 1：</strong></p>

<p><img alt="" src="https://assets.leetcode.com/uploads/2019/10/31/sample_3_1610.png" style="height: 151px; width: 240px;" /></p>

<pre>
<strong>输入：</strong>grid = [[1,1,1,1,1,1,1,0],[1,0,0,0,0,1,1,0],[1,0,1,0,1,1,1,0],[1,0,0,0,0,1,0,1],[1,1,1,1,1,1,1,0]]
<strong>输出：</strong>2
<strong>解释：</strong>
灰色区域的岛屿是封闭岛屿，因为这座岛屿完全被水域包围（即被 1 区域包围）。</pre>

<p><strong>示例 2：</strong></p>

<p><img src="https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2019/11/07/sample_4_1610.png" style="height: 98px; width: 160px;" /></p>

<pre>
<strong>输入：</strong>grid = [[0,0,1,0,0],[0,1,0,1,0],[0,1,1,1,0]]
<strong>输出：</strong>1
</pre>

<p><strong>示例 3：</strong></p>

<pre>
<strong>输入：</strong>grid = [[1,1,1,1,1,1,1],
&nbsp;            [1,0,0,0,0,0,1],
&nbsp;            [1,0,1,1,1,0,1],
&nbsp;            [1,0,1,0,1,0,1],
&nbsp;            [1,0,1,1,1,0,1],
&nbsp;            [1,0,0,0,0,0,1],
             [1,1,1,1,1,1,1]]
<strong>输出：</strong>2
</pre>

<p>&nbsp;</p>

<p><strong>提示：</strong></p>

<ul>
	<li><code>1 &lt;= grid.length, grid[0].length &lt;= 100</code></li>
	<li><code>0 &lt;= grid[i][j] &lt;=1</code></li>
</ul>
<div><div>Related Topics</div><div><li>深度优先搜索</li><li>广度优先搜索</li><li>并查集</li><li>数组</li><li>矩阵</li></div></div><br><div><li>👍 144</li><li>👎 0</li></div>
*/

//leetcode submit region begin(Prohibit modification and deletion)
class Solution {
    public int closedIsland(int[][] grid) {
        int m = grid.length;
        int n = grid[0].length;

        //提前淹没靠近陆地的岛屿
        for (int i = 0; i < m; i++) {
            dfs(grid,i,0);
            dfs(grid,i,n-1);
        }

        //提前淹没靠近陆地的岛屿
        for (int j = 0; j < n; j++) {
            dfs(grid,0,j);
            dfs(grid,m-1,j);
        }

        int res = 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j <n; j++) {
                if(grid[i][j]==0    ){
                    res++;
                    dfs(grid,i,j);
                }
            }
        }
        return res;
    }

    void dfs(int[][] grid,int i,int j){


        int m = grid.length;
        int n = grid[0].length;

        if (i < 0 || j < 0 || i >= m || j >= n) {
            return;
        }

        //是水
        if(grid[i][j]==1){
            return;
        }

        grid[i][j] = 1;

        // 淹没上下左右的陆地
        dfs(grid, i + 1, j);
        dfs(grid, i, j + 1);
        dfs(grid, i - 1, j);
        dfs(grid, i, j - 1);

    }
}
//leetcode submit region end(Prohibit modification and deletion)