# Number of Islands

LintCode-433.Number of Islands

Given a boolean 2D matrix, find the number of islands.

Notice:
0 is represented as the sea, 1 is represented as the island. If two 1 is adjacent, we consider them in the same island. We only consider up/down/left/right adjacent.

Given graph:

``````[
[1, 1, 0, 0, 0],
[0, 1, 0, 0, 1],
[0, 0, 0, 1, 1],
[0, 0, 0, 0, 0],
[0, 0, 0, 0, 1]
]
return 3.
``````
``````public class Solution {
/**
* @param grid a boolean 2D matrix
* @return an integer
*/
public int numIslands(boolean[][] grid) {
if (grid == null || grid.length == 0 || grid[0].length == 0) {
return 0;
}

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

int result = 0;
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
if (grid[i][j] == false) {
continue;
}

result++;
dfs(grid, i, j);
}
}

return result;
}

void dfs(boolean[][] grid, int i, int j) {
if (i < 0 || i >= grid.length || j < 0 || j >= grid[0].length) {
return;
}

if (grid[i][j] == true) {
grid[i][j] = false;
dfs(grid, i, j - 1);
dfs(grid, i, j + 1);
dfs(grid, i - 1, j);
dfs(grid, i + 1, j);
}
}
}
``````

Hope this helps,
Michael