# JavaScript實現從陣列中選出和等於固定值的n個數

``````
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;
}``````

array: 資料來源陣列。必選。

sum: 相加的和。必選。

tolerance: 容差。如果不指定此引數，則相加的和必須等於sum引數，指定此引數可以使結果在容差範圍內浮動。可選。

targetCount: 運算元數量。如果不指定此引數，則結果包含所有可能的情況，指定此引數可以篩選出固定數量的數相加，假如指定為3，那麼結果只包含三個數相加的情況。可選。