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/*
695. 岛屿的最大面积
给定一个包含了一些 0 和 1的非空二维数组 grid , 一个 岛屿 是由四个方向 (水平或垂直) 的 1 (代表土地) 构成的组合。你可以假设二维矩阵的四个边缘都被水包围着。
找到给定的二维数组中最大的岛屿面积。(如果没有岛屿，则返回面积为0。)
示例 1:
[[0,0,1,0,0,0,0,1,0,0,0,0,0],
[0,0,0,0,0,0,0,1,1,1,0,0,0],
[0,1,1,0,1,0,0,0,0,0,0,0,0],
[0,1,0,0,1,1,0,0,1,0,1,0,0],
[0,1,0,0,1,1,0,0,1,1,1,0,0],
[0,0,0,0,0,0,0,0,0,0,1,0,0],
[0,0,0,0,0,0,0,1,1,1,0,0,0],
[0,0,0,0,0,0,0,1,1,0,0,0,0]]
对于上面这个给定矩阵应返回 6。注意答案不应该是11，因为岛屿只能包含水平或垂直的四个方向的‘1’。
示例 2:
[[0,0,0,0,0,0,0,0]]
对于上面这个给定的矩阵, 返回 0。
注意: 给定的矩阵grid 的长度和宽度都不超过 50。
来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/max-area-of-island
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。
*/
package graph;
public class MaxAreaOfIsland {
static int[][] dirs = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
public static int maxAreaOfIsland(int[][] grid) {
boolean[][] visited = new boolean[grid.length][grid[0].length];
int max = 0;
for (int i = 0; i < grid.length; i++) {
for (int j = 0; j < grid[0].length; j++) {
if (!visited[i][j] && grid[i][j] == 1) {
int area = dfs(grid, visited, i, j);
max = Math.max(max, area);
}
}
}
return max;
}
private static int dfs(int[][] grid, boolean[][] visited, int x, int y) {
visited[x][y] = true;
int area = 1;
for (int[] pair : dirs) {
int nx = x + pair[0];
int ny = y + pair[1];
if (nx >= 0 && nx < grid.length && ny >= 0 && ny < grid[0].length && !visited[nx][ny] && grid[nx][ny] == 1) {
area += dfs(grid, visited, nx, ny);
}
}
return area;
}
}