使用堆实现Top K 算法 JS 实现

1. 堆算法Top，时间复杂度 O(LogN)

function top(arr,comp){
if(arr.length == 0){return ;}
var i = arr.length / 2 | 0 ;
for(;i >= 0; i--){
if(comp(arr[i], arr[i * 2])){exch(arr, i, i*2);}
if(comp(arr[i], arr[i * 2 + 1])) {exch(arr, i, i*2 + 1);}
}
return arr[0];


}


function exch(arr,i,j){
var t = arr[i];
arr[i] = arr[j];
arr[j] = t;
}

2. 调用K次堆实现，时间复杂度为 O(K * LogN)

function topK(arr,n,comp){
if(!arr || arr.length == 0 || n <=0 || n > arr.length){
return -1;
}


var ret  = new Array();
for(var i = 0;i < n; i++){
var max = top(arr,comp);
ret.push(max);
arr.splice(0,1);
}
return ret;
}

3.測试

var ret = topK(new Array(16,22,91,0,51,44,23),3,function (a,b){return a < b;});
console.log(ret);