findJob.js

const ACTIVITIES = [
  {name: 'side-project', time: 10, xp: 12},
  {name: 'algorithms', time: 3, xp: 7},
  {name: 'networking', time: 1, xp: 0.5},
  {name: 'exercise', time: 2, xp: 1.5},
  {name: 'systems design', time: 4, xp: 4},
  {name: 'making CSS codepens', time: 3, xp: 4}
];



function findJob(time){
  if(time==0){
    return [];
  }
  const availibleActivities=ACTIVITIES.filter(activity=>activity.time<=time);
  let max=0;
  let arr=[];
  availibleActivities.forEach(item=>{
    
    const q=Math.floor(time/item.time);
    const xp=item.xp*q;
    const remainingXP=findJob(time-item.time*q);
    const sum=remainingXP.reduce((result,item)=>{return (item.qty||0)*item.xp+result},xp);
    if(max<sum){
      max=sum;
      item.qty=q;
      arr=[...remainingXP,item];
      return sum
    }
  })  
  return arr;
}

const TIME=6;

console.time('findJob');
const result=findJob(TIME, ACTIVITIES)
console.timeEnd('findJob');
console.log('findJob',result);