function sum(arr) { let sum = 0; for (let i = 0; i < arr.length; i++) { for (let j = 0; j < arr[i].length; j++) { sum += arr[i][j]; } } return sum; }
function sum(arr) { let sum = 0; for (let i = 0; i < arr.length; i++) { for (let j = 0; j < arr[i].length; j++) { sum += arr[i][j]; } } return sum; }