如何解决从一组中找到给出最少废物量的数字
|| 将一个集合传递到下面的此方法，并且还传递一个条的长度。如果从该条的长度中删除了该集合中的某些数字，则解决方案应该输出该集合中的数字，这些数字将提供最少的浪费。因此，条形长度10，集合包括6,1,4，因此解为6和4，浪费为0。我在通过集合回溯的条件上遇到了一些麻烦。香港专业教育学院也试图使用浪费的“全局”变量来帮助回溯方面，但无济于事。 SetInt是一个手工制作的集合实现，可以添加，删除，检查集合是否为空并从集合中返回最小值。/*
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package recback;
public class RecBack {
public static int WASTAGE = 10;
public static void main(String[] args) {
int[] nums = {6,4};
//Order Numbers
int barLength = 10;
//Bar length
SetInt possibleOrders = new SetInt(nums.length);
SetInt solution = new SetInt(nums.length);
//Set Declarration
for (int i = 0; i < nums.length; i++)possibleOrders.add(nums[i]);
//Populate Set
SetInt result = tryCutting(possibleOrders,solution,barLength);
result.printNumbers();
}
private static SetInt tryCutting(SetInt possibleOrders,SetInt solution,int lengthleft)
{
SetInt clonedSet = possibleOrders.cloneSet(); //initialise selection of candidates
for (int i = 0; i < possibleOrders.numberInSet(); i++) // the repeat
{
int a = clonedSet.min(); //select next candidate
if (a <= lengthleft) //if accecptable
{
solution.add(a); //record candidate
lengthleft -= a;
clonedSet.remove(a); //remove from original set
if (!clonedSet.isEmpty()) //solution not complete
{
WASTAGE +=a;
tryCutting(clonedSet,lengthleft);//try recursive call
if (lengthleft > WASTAGE)//if not successfull
{
WASTAGE += a;
solution.remove(a);
}
} //solution not complete
}
} //for loop
return solution;
}
}
解决方法
你有几个问题。
一个是这一行：
int a = clonedSet.min(); //select next candidate
WASTAGE +=a;
for (int i = 0; i < possibleOrders.numberInSet(); i++) // the repeat
max
min
public static void main(String[] args) {
int[] nums = {6,1,4}; //Order Numbers
int barLength = 10; //Bar length
bestSolution = new HashSet<SetInt>();
bestWastage = barLength;
SetInt possibleOrders = new SetInt(nums.length);
SetInt solution = new SetInt(nums.length); //Set Declarration
for (int i = 0; i < nums.length; i++) {
possibleOrders.add(nums[i]); //Populate Set
}
tryCutting(possibleOrders,solution,barLength);
for (SetInt result : bestSolution) {
result.printNumbers();
}
}
private static int bestWastage;
private static Set<SetInt> bestSolution;
private static void tryCutting(SetInt possibleOrders,SetInt solution,int lengthleft) {
if (lengthleft < bestWastage) {
// Better than the best solution
bestWastage = lengthleft;
bestSolution.clear();
bestSolution.add(solution.cloneSet());
} else if (lengthleft == bestWastage) {
// Just as good as the best solution
bestSolution.add(solution.cloneSet());
}
int a = possibleOrders.min(); //select next candidate
if (a <= lengthleft) { // If acceptable
possibleOrders.remove(a); // Remove it
tryCutting(possibleOrders,lengthleft); // Try without that cut
solution.add(a); // add to the solution
tryCutting(possibleOrders,lengthleft - a); // Try with that cut
solution.remove(a); // remove again
possibleOrders.add(a); // add the candidate back on again
}
}
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