200.js

/** ------------------------------------------------------------------------------
 * 
 * 200. Number of Islands
 * Topics: Array, Depth-First Search, Breadth-First Search, Matrix
 * https://leetcode.com/problems/number-of-islands/description/
 * 
 ------------------------------------------------------------------------------ */
/**
 * @param {character[][]} grid
 * @return {number}
 */
var numIslands = function (grid) {
  if (!grid || grid.length === 0) return 0

  const rows = grid.length
  const cols = grid[0].length
  let count = 0

  const dfs = (r, c) => {
    if (r < 0 || r >= rows || c < 0 || c >= cols || grid[r][c] === "0") {
      return
    }

    grid[r][c] = "0"
    dfs(r + 1, c)
    dfs(r - 1, c)
    dfs(r, c + 1)
    dfs(r, c - 1)
  }

  for (let i = 0; i < rows; i++) {
    for (let j = 0; j < cols; j++) {
      if (grid[i][j] === "1") {
        count++
        dfs(i, j)
      }
    }
  }

  return count
}

console.log(
  numIslands([
    ["1", "1", "1", "1", "0"],
    ["1", "1", "0", "1", "0"],
    ["1", "1", "0", "0", "0"],
    ["0", "0", "0", "0", "0"],
  ]),
)