排个序，求前k个元素和即可
int minimum(int K, vector <int> danceCost)
{
sort(danceCost.begin(),danceCost.end());
return accumulate(danceCost.begin(),danceCost.begin()+K,0);
}
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topcoder SRM 624 DIV2 CostOfDancing
原文：http://www.cnblogs.com/xiongqiangcs/p/3785424.html