algorithm - Find keys of the 3 largest values in a Javascript Object with O(n) complexity? -

say have object such as:

let objtocheck = {   a: 2,    b: 5,   c: 9,   d: 33,   e: 4,   f: 8,   g: 3,   h: 10 }; 

how go returning keys of 3 largest values in ascending order, in case be: [ 'c', 'h', 'd' ], in linear time? evidently need loop through entire object once compare values, i'm having troubling coming solution doesn't involve nested loops believe o(n²). here solution looks far:

function findbig3(obj){   const res = [];   const largest = object.values(obj).sort((a,b) => {return b-a}).slice(0,3);    (let key in obj){     largest.foreach( (val) => {       if (obj[key] === val) res.push(key);     });   }   return res; } 

i imagine need declare 3 variables, such big1, big2, big3, , loop through object type of comparison check , reassign appropriate, i'm struggling implementation.

this algorithm runs in o(n).

function getthreelargestkeys(obj){     var k1, k2, k3;     var v1, v2, v3;     v1 = v2 = v3 = -infinity;      // o(1)     var insertkey = function(key){         var value = obj[key];  // note 1          // note 2         if(value >= v1){             v3 = v2; v2 = v1; v1 = value;             k3 = k2; k2 = k1; k1 = key;         }else if(value >= v2){             v3 = v2; v2 = value;             k3 = k2; k2 = key;         }else if(value >= v3){             v3 = value;             k3 = key;         }     };      // o(n)     for(var key in obj){         // note 3         insertkey(key);     }      return [k1, k2, k3]; } 

https://jsfiddle.net/derekl/pzatq729/

please not copy-paste code right homework solution. rewrite code once understand it.

note:

1. this assumes object lookup o(1). depends on how implemented in interpreter, lower o(log n).
2. these conditionals can optimized. leave practice reader.
3. normally should check if key owned object instance, here assume input object not inherited object.prototype.