rotateMatrixBy90
JavaScript
function rotate(a){
return a.map((row,i) =>{
return row.map((val,j)=>a[a.length-1-j][i])
});
}
let a = [[1,2,3,4], [5,6,7,8], [9,10,11,12], [13,14,15,16]];
console.table(a);
console.table(rotate(a))
console.log(rotate(a))