JavaScript实现从数组中选出和等于固定值的n个数

function getCombBySum(array,sum,tolerance,targetCount){
var util = {
/*
get combination from array
arr: target array
num: combination item length
return: one array that contain combination arrays
*/
getCombination: function(arr, num) {
var r=[];
(function f(t,a,n)
{
if (n==0)
{
return r.push(t);
}
for (var i=0,l=a.length; i<=l-n; i++)
{
f(t.concat(a[i]), a.slice(i+1), n-1);
}
})([],arr,num);
return r;
},
//take array index to a array
getArrayIndex: function(array) {
var i = 0,
r = [];
for(i = 0;i<array.length;i++){
r.push(i);
}

return r;
}
},logic = {
//sort the array,then get what's we need
init: function(array,sum) {
//clone array
var _array = array.concat(),
r = [],
i = 0;
//sort by asc
_array.sort(function(a,b){
return a - b;
});
//get all number when it's less than or equal sum
for(i = 0;i<_array.length;i++){
if(_array[i]<=sum){
r.push(_array[i]);
}else{
break;
}
}

return r;
},
//important function
core: function(array,sum,arrayIndex,count,r){
var i = 0,
k = 0,
combArray = [],
_sum = 0,
_cca = [],
_cache = [];

if(count == _returnMark){
return;
}
//get current count combination
combArray = util.getCombination(arrayIndex,count);
for(i = 0;i<combArray.length;i++){
_cca = combArray[i];
_sum = 0;
_cache = [];
//calculate the sum from combination
for(k = 0;k<_cca.length;k++){
_sum += array[_cca[k]];
_cache.push(array[_cca[k]]);
}
if(Math.abs(_sum-sum) <= _tolerance){
r.push(_cache);
} 
}

logic.core(array,sum,arrayIndex,count-1,r);
}

},
r = [],
_array = [],
_targetCount = 0,
_tolerance = 0,
_returnMark = 0;

//check data
_targetCount = targetCount || _targetCount;
_tolerance = tolerance || _tolerance;

_array = logic.init(array,sum);
if(_targetCount){
_returnMark = _targetCount-1;
}

logic.core(_array,sum,util.getArrayIndex(_array),(_targetCount || _array.length),r);

return r;
}