#200. 岛屿数量

var numIslands = function (grid) {
  const rows = grid.length;
  const columns = grid[0].length;
  const directions = [
    [1, 0],
    [-1, 0],
    [0, 1],
    [0, -1],
  ];
  let count = 0;

  const bfs = (startRow, startColumn) => {
    const queue = [[startRow, startColumn]];
    let head = 0;

    // 入队时立即标记，避免被相邻格重复入队
    grid[startRow][startColumn] = "0";

    while (head < queue.length) {
      const [row, column] = queue[head++];

      for (const [rowOffset, columnOffset] of directions) {
        const nextRow = row + rowOffset;
        const nextColumn = column + columnOffset;
        const isInGrid =
          nextRow >= 0 &&
          nextRow < rows &&
          nextColumn >= 0 &&
          nextColumn < columns;

        if (isInGrid && grid[nextRow][nextColumn] === "1") {
          grid[nextRow][nextColumn] = "0";
          queue.push([nextRow, nextColumn]);
        }
      }
    }
  };

  for (let row = 0; row < rows; row++) {
    for (let column = 0; column < columns; column++) {
      if (grid[row][column] === "1") {
        count++;
        bfs(row, column);
      }
    }
  }

  return count;
};