对于我的数据结构课程中的一个项目，我的任务是创建一个 3 维范围树，其中每个维度都是 BST。我读这个问题，但这是一个Android问题，而且我们问题的原因似乎不同，唯一的答案是不被接受。
代码墙即将推出。对不起。
涉及班级：
-
Point3D<T>：包含点坐标的通用类。T extends Comparable<T>, and Point3D也扩展它
-
RangeTree<T>：包含整个树的根以及构建和搜索树的方法的通用类
有比这两个更多的类，但它们似乎与我收到 ConcurrentModificationException 的原因无关（链接到芝商所）。
这是我运行驱动程序时得到的结果：
Read in 10 points //Number of points read in driver, this is okay
5//first median, 10 / 2
2//second median 5 / 2
first[0.082 0.791 0.832 , 0.366 0.136 0.009 ]//correct
second[0.138 0.968 0.391 , 0.414 0.785 0.883 , 0.546 0.044 0.133 ]//correct
merged[0.082 0.791 0.832 , 0.366 0.136 0.009 ]//not correct
first[0.082 0.791 0.832 , 0.366 0.136 0.009 ]//printed again. why?
2//secondHalf being sorted
first[0.415 0.64 0.099 , 0.513 0.612 0.466 ]//correct
second[0.091 0.719 0.772 , 0.199 0.999 0.086 , 0.896 0.835 0.86 ]//correct
Exception in thread "main" java.util.ConcurrentModificationException
at java.util.ArrayList$SubList.checkForComodification(ArrayList.java:1231)
at java.util.ArrayList$SubList.size(ArrayList.java:1040)
at RangeTree.mergeList(RangeTree.java:189)
at RangeTree.sortAscending(RangeTree.java:175)
at RangeTree.sortAscending(RangeTree.java:173)
at RangeTree.build3DTree(RangeTree.java:126)
at RangeTree.build(RangeTree.java:11)
at Main.main(Main.java:35)
When RangeTree.build被称为(Main.java:35)，它需要一个List<Point3D<T>>并将其传递给RangeTree.build3DTree(RangeTree.java:11) 它还需要剩余 # 个维度来构建，以及一个指示是否List已经排序了。该方法中的 RangeTree.java:126 是我调用的行sortAscending in build3DTree.
sortAscending（它是递归的）通过比较某个维度上的点来完成听起来的样子，从x(x = 0, y = 1, z = 2)，如果它们相等，它会检查下一个维度等。基于上述，它显然工作得很好，除了那个奇怪的故障Line 172以某种方式打印两次。下面是sortAscending代码（所有打印行纯粹用于调试）：
private List<Point3D<T>> sortAscending(List<Point3D<T>> pointArr){
if(pointArr.size() <= 3){//minimum sublist size is 3
int median = findMedian(pointArr);
Point3D<T> medianElement = pointArr.get(median);//retrieves coordinate to sort on
int compareLeft = medianElement.compareTo(pointArr.get(median - 1));
if(compareLeft < 0){//determine if median is less than element to its left. There will always be an element to the left
pointArr.add(0, pointArr.remove(median));
medianElement = pointArr.get(median);
}
try{//check median against element to its right. May not be valid if sublist is size 2
int compareRight = medianElement.compareTo(pointArr.get(median + 1));
if(compareRight > 0){
Point3D<T> rightEnd = pointArr.get(median + 1);
Point3D<T> leftEnd = pointArr.get(median - 1);
if(rightEnd.compareTo(leftEnd) < 0)
pointArr.add(0, pointArr.remove(median + 1));
else
pointArr.add(median, pointArr.remove(median + 1));
}
} catch (IndexOutOfBoundsException e){
}
return pointArr;
}
int median = findMedian(pointArr);//returns pointArr.size() / 2
System.out.println(median);//for debugging
List<Point3D<T>> firstHalf = sortAscending(pointArr.subList(0, median));
System.out.println("first" + firstHalf); //prints twice, once when it should, and again after Line 176 prints
List<Point3D<T>> secondHalf = sortAscending(pointArr.subList(median, pointArr.size()));//Line 173
System.out.println("second" + secondHalf);//debugging
List<Point3D<T>> merged = mergeList(firstHalf, secondHalf);//Line 175
System.out.println("merged" + merged);//debugging
return merged;//mergeList(firstHalf, secondHalf);
}
所以，CME 的最终来源似乎是在mergeList，并且直到调用后半部分数据才中断。mergeList（迭代）需要两个List<Point3D<T>>并将它们合并成一个按升序排序的列表，然后返回。也就是说，它采用第一个参数并将其修改为合并列表并返回它。代码：
private List<Point3D<T>> mergeList(List<Point3D<T>> firstList, List<Point3D<T>> secList){
int sListSize = secList.size();
int fListSize = firstList.size();//Line 188
Point3D<T> firstListElement = firstList.get(fListSize - 1);
Point3D<T> secListElement = secList.get(0);
if(secListElement.compareTo(firstListElement) >= 0){//check to see if secList can be appended to end of firstList e.g. firstList = {1, 2} secList = {3, 4, 5}
firstList.addAll(secList);
return firstList;
}
secListElement = secList.get(secList.size() - 1);
firstListElement = firstList.get(0);
if(secListElement.compareTo(firstListElement) <= 0){//check to see if firstList can be appended to the end of secList e.g. secList = {1, 2} firstList = {3,4,5}
secList.addAll(firstList);
return secList;
}
for(int a = 0; a < secList.size(); a++){//take an element from secList and insert it into firstList
secListElement = secList.get(a);
int minIdx, maxIdx, median = findMedian(firstList);
int mComp = secListElement.compareTo(firstList.get(median));//compare to the median of firstList to choose side to start from
if(mComp < 0){
minIdx = 0;
maxIdx = median;
}
else if(mComp > 0){
minIdx = median;
maxIdx = firstList.size();
}
else{//if mComp is 0, insert it at median index
firstList.add(median, secList.get(a));
continue;
}
for(; minIdx < maxIdx; minIdx++){
firstListElement = firstList.get(minIdx);
int compare = secListElement.compareTo(firstListElement);
if(compare <= 0){
firstList.add(minIdx, secList.get(a));
break;
}
}
}
return firstList;
}
因此，由于某种原因，当我尝试访问的大小时，CME 出现了firstList。我不知道为什么会发生这种情况。我已经使用数据集（下面发布）手动跟踪了我的代码，完成了每个步骤，但我看不到 CME 来自哪里。数据：
10
0.366 0.136 0.009
0.082 0.791 0.832//beautiful 3D points
0.138 0.968 0.391
0.414 0.785 0.883
0.546 0.044 0.133
0.513 0.612 0.466
0.415 0.640 0.099
0.199 0.999 0.086
0.896 0.835 0.860
0.091 0.719 0.772
0.25 0.75 0.25 0.75 0.25 0.75//range queries. Code fails before we get to this
0.75 0.25 0.8 0.1 0.9 0.1
0.95 1.75 0.1 0.01 0.1 0.2
exit//no more queries
