numberofislands.js

// * Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. 
// An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.
// *
// * Example 1:
// *
// * Input:
// * 11110
// * 11010
// * 11000
// * 00000
// *
// * Output: 1
// * Example 2:
// *
// * Input:
// * 11000
// * 11000
// * 00100
// * 00011
// *
// * Output: 3
// */

// /**
// * @param {character[][]} grid
// * @return {number}
// */
let numIslands = function(grid) {
  let markIsland = function(grid, x, y, visited) {
      // this is an error boundary to ensure that we iterate within the confine grid area.
    if (x < 0 || x > grid.length - 1 || y < 0 || y > grid[x].length - 1) {
      return;
    }
    if (visited[x][y] === true) {
      return;
    }
    visited[x][y] = true;
    if (grid[x][y] === "0") {
      return;
    }
    markIsland(grid, x - 1, y, visited);
    markIsland(grid, x + 1, y, visited);
    markIsland(grid, x, y - 1, visited);
    markIsland(grid, x, y + 1, visited);
  };

  let visited = [];
  for (let i = 0; i < grid.length; i++) {
    visited[i] = [];
  }
  let count = 0;
  for (let x = 0; x < grid.length; x++) {
    for (let y = 0; y < grid[x].length; y++) {
      if (!visited[x][y] && grid[x][y] === "1") {
        count++;
        markIsland(grid, x, y, visited);
      }
      visited[x][y] = true;
    }
  }
  return count;
};

let example2 = [
  ["1", "1", "0", "0", "1"],
  ["1", "1", "0", "0", "0"],
  ["0", "0", "0", "0", "0"],
  ["1", "0", "0", "1", "1"],
  ["1", "0", "0", "1", "1"]
];