200. Number of Islands

/*
 * Explore the island and delete the parts we have explored while exploring
 * Therefore every '1' we hit must be a new island
 */

class Solution {

  public int numIslands(char[][] grid) {
    int rows = grid.length;
    if (rows == 0) return 0;

    int cols = grid[0].length;

    int islands = 0;

    for (int row = 0; row < rows; row++) {
      for (int col = 0; col < cols; col++) {
        if (grid[row][col] == '1') {
          updateGrid(grid, row, col);
          islands++;
        }
      }
    }

    return islands;
  }

  public static void updateGrid(char[][] grid, int row, int col) {
    int rows = grid.length;
    int cols = grid[0].length;

    if (!isWithinBounds(grid, row, col) || grid[row][col] == '0') return;

    grid[row][col] = '0';

    updateGrid(grid, row, col + 1);
    updateGrid(grid, row + 1, col);
    updateGrid(grid, row, col - 1);
    updateGrid(grid, row - 1, col);
  }

  public static boolean isWithinBounds(char[][] grid, int row, int col) {
    return
      grid.length > 0 &&
      row >= 0 &&
      col >= 0 &&
      row < grid.length &&
      col < grid[0].length;
  }
}