463.js

/** ------------------------------------------------------------------------------
 * 
 * 463. Island Perimeter
 * Topics: Matrix
 * https://leetcode.com/problems/island-perimeter/?envType=problem-list-v2&envId=matrix
 * 
 ------------------------------------------------------------------------------ */
/**
 * @param {number[][]} grid
 * @return {number}
 */
var islandPerimeter = function (grid) {
  const row = grid.length
  const col = grid[0].length

  let count = 0

  for (let i = 0; i < row; i++) {
    for (let j = 0; j < col; j++) {
      if (grid[i][j] === 0) continue

      count += 4
      if (j > 0 && grid[i][j - 1]) {
        count -= 2
      }
      if (i > 0 && grid[i - 1][j]) {
        count -= 2
      }
    }
  }
  return count
}

console.log(
  islandPerimeter([
    [0, 1, 0, 0],
    [1, 1, 1, 0],
    [0, 1, 0, 0],
    [1, 1, 0, 0],
  ]),
)