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Polygon Perimeter

Description

You have a rectangular white board with some black cells. The black cells create a connected black figure, i.e. it is possible to get from any black cell to any other one through connected adjacent (sharing a common side) black cells.

Find the perimeter of the black figure assuming that a single cell has unit length.

It’s guaranteed that there is at least one black cell on the table.

Example

  • For

    matrix = [[false, true, true ], [true, true, false], [true, false, false]]

    the output should be

    polygonPerimeter(matrix) = 12.

  • For

    matrix = [[true, true, true], [true, false, true], [true, true, true]]

    the output should be

    polygonPerimeter(matrix) = 16.

    </code>

Input/Output

  • [execution time limit] 4 seconds (js)

  • [input] array.array.boolean matrix

    A matrix of booleans representing the rectangular board where true means a black cell and false means a white one.

    Guaranteed constraints:
    2 ≤ matrix.length ≤ 5,
    2 ≤ matrix[0].length ≤ 5.

  • [output] integer

[JavaScript (ES6)] Syntax Tips

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// Prints help message to the console
// Returns a string
function helloWorld(name) {
console.log("This prints to the console when you Run Tests");
return "Hello, " + name;
}

Solution

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function polygonPerimeter(matrix) {
  var adjacents = (i, j) => [
    [i - 1, j],
    [i, j - 1],
    [i, j + 1],
    [i + 1, j],
  ];
  var perimeter = 0;
  for (var i = 0; i < matrix.length; i++) {
    for (var j = 0; j < matrix[0].length; j++) {
      perimeter +=
        matrix[i][j] &&
        adjacents(i, j).reduce(function (acc, pos) {
          return (
            acc +
            (pos[0] < 0 ||
              pos[1] < 0 ||
              pos[0] == matrix.length ||
              pos[1] === matrix[0].length ||
              !matrix[pos[0]][pos[1]])
          );
        }, 0);
    }
  }
  return perimeter;
}