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Problem1.java
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Problem1.java
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// Time Complexity : O(m*n)
// Space Complexity : O(m*n)
// Did this code successfully run on Leetcode : Yes
// Any problem you faced while coding this : No
// Your code here along with comments explaining your approach
class Solution {
public int numIslands(char[][] grid) {
if (grid == null || grid.length == 0) {
return 0;
}
int numIslands = 0;
int rows = grid.length;
int cols = grid[0].length;
// Traverse through every cell in the grid
for (int i = 0; i < rows; i++) {
for (int j = 0; j < cols; j++) {
// If a '1' is found, it's the start of a new island
if (grid[i][j] == '1') {
numIslands++;
dfs(grid, i, j); // Perform DFS to mark the entire island
}
}
}
return numIslands;
}
// Helper method to perform DFS
private void dfs(char[][] grid, int row, int col) {
int rows = grid.length;
int cols = grid[0].length;
// Base condition to stop DFS
if (row < 0 || col < 0 || row >= rows || col >= cols || grid[row][col] == '0') {
return;
}
// Mark the current cell as visited
grid[row][col] = '0';
// Explore all 4 directions
dfs(grid, row + 1, col); // Down
dfs(grid, row - 1, col); // Up
dfs(grid, row, col + 1); // Right
dfs(grid, row, col - 1); // Left
}
}