Matrix sum of border elements

by Saksham Malhotra

JavaScript

var arr = [
  [1, 1, 1, 1, 1],
  [2, 2, 2, 2, 2],
  [3, 3, 3, 3, 3]
]

var sum = arr.reduce((acc, val, index) => {
  if (index == 0 || index == arr.length - 1)
    return acc += val.reduce((a, b) => a + b);
	else
  	return acc += val[0] + val[val.length - 1];
}, 0);

console.log(sum);