#1020 - Number of Enclaves

Medium • View on LeetCode • View on GitHub

Array Depth-First Search Matrix Breadth-First Search Union Find

Problem Description

You are given an m x n binary matrix grid, where 0 represents a sea cell and 1 represents a land cell.

A move consists of walking from one land cell to another adjacent (4-directionally) land cell or walking off the boundary of the grid.

Return the number of land cells in grid for which we cannot walk off the boundary of the grid in any number of moves.

Solution

/**
 * @param {number[][]} grid
 * @return {number}
 */
var numEnclaves = function(grid) {
  const rows = grid.length;
  const cols = grid[0].length;

  for (let i = 0; i < rows; i++) {
    exploreBoundary(i, 0);
    exploreBoundary(i, cols - 1);
  }

  for (let j = 0; j < cols; j++) {
    exploreBoundary(0, j);
    exploreBoundary(rows - 1, j);
  }

  let result = 0;
  for (let i = 0; i < rows; i++) {
    for (let j = 0; j < cols; j++) {
      result += grid[i][j];
    }
  }

  return result;

  function exploreBoundary(row, col) {
    if (row < 0 || row >= rows || col < 0 || col >= cols || grid[row][col] !== 1) return;
    grid[row][col] = 0;
    exploreBoundary(row + 1, col);
    exploreBoundary(row - 1, col);
    exploreBoundary(row, col + 1);
    exploreBoundary(row, col - 1);
  }
};