【发布时间】：2018-12-02 20:17:40
【问题描述】：
我是一名计算机科学专业的学生，我正在尝试学习 Java 中的 Quicksort。我实现了自己的版本，我确信它可能不是最好的实现，所以不要对我太苛刻，这是为了学习目的。为了学习，我想知道为什么我的快速排序给我以下错误，我似乎无法解决或理解。提前谢谢！
Exception in thread "main" java.lang.StackOverflowError
at java.io.FileOutputStream.write(FileOutputStream.java:326)
at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:82)
at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:140)
at java.io.PrintStream.write(PrintStream.java:482)
at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:221)
at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:291)
at sun.nio.cs.StreamEncoder.flushBuffer(StreamEncoder.java:104)
at java.io.OutputStreamWriter.flushBuffer(OutputStreamWriter.java:185)
at java.io.PrintStream.write(PrintStream.java:527)
at java.io.PrintStream.print(PrintStream.java:669)
at java.io.PrintStream.println(PrintStream.java:806)
at myQuickSort.mySwapMethod(myQuickSort.java:116)
at myQuickSort.partition(myQuickSort.java:52)
at myQuickSort.myQuickSortMethod(myQuickSort.java:39)
at myQuickSort.myQuickSortMethod(myQuickSort.java:40)
at myQuickSort.myQuickSortMethod(myQuickSort.java:40)
我的 Java 快速排序实现：
public class myQuickSort {
private int[] array;
public static void main(String[] args) {
int[] array = new int[] {3,5,74,3,67,45,23,6,34,12,889,4,25,1,0,7,4};
myQuickSort test = new myQuickSort(array);
System.out.println("Before:");
for(int i =0; i < array.length;i++) {
System.out.print(array[i]+",");
}
System.out.println("\n");
test.myQuickSortMethod(0, array.length -1);
System.out.println("After:");
for(int i =0; i < array.length;i++) {
System.out.print(array[i]+",");
}
}
public myQuickSort(int[] array) {
this.array = array;
}
public void myQuickSortMethod(int indexStart, int indexEnd) {
if(indexStart == indexEnd) {
return;
}
int whereToSplit = partition(indexStart,indexEnd);
myQuickSortMethod(indexStart, whereToSplit-1);
myQuickSortMethod(whereToSplit+1,indexEnd);
}
private int partition(int indexStart, int indexEnd) {
int leftOfPivotIndex = indexStart; //left pointer
int rightOfPivotIndex = indexEnd; //right pointer
int pivotIndex =indexStart+(indexEnd-indexStart)/2; //pivot chosen from the middle of the list
//swapping pivot with the first element of the array
mySwapMethod(indexStart,pivotIndex);
pivotIndex = indexStart;
if(indexStart != indexEnd) {
leftOfPivotIndex++;
}
while(leftOfPivotIndex <= rightOfPivotIndex) {
//left - pointer
while(array[leftOfPivotIndex] < array[pivotIndex] && leftOfPivotIndex < rightOfPivotIndex ) {
leftOfPivotIndex++;
}
//right-pointer loop
while(array[rightOfPivotIndex] >= array[pivotIndex] && leftOfPivotIndex < rightOfPivotIndex ) {
rightOfPivotIndex--;
}
mySwapMethod(leftOfPivotIndex,rightOfPivotIndex);
if(leftOfPivotIndex == rightOfPivotIndex) {
System.out.println("BREAKING CASE");
if(array[leftOfPivotIndex] <= array[pivotIndex]) {
mySwapMethod(pivotIndex,leftOfPivotIndex);
return leftOfPivotIndex;
}else {
mySwapMethod(pivotIndex,leftOfPivotIndex -1);
return leftOfPivotIndex -1;
}
}else {
//Move both left and write pointers after the swap
leftOfPivotIndex++;
rightOfPivotIndex--;
}
if(leftOfPivotIndex == rightOfPivotIndex || leftOfPivotIndex > rightOfPivotIndex) {
System.out.println("BREAKING CASE");
if(array[leftOfPivotIndex] < array[pivotIndex]) {
mySwapMethod(pivotIndex,leftOfPivotIndex);
return leftOfPivotIndex;
}else {
mySwapMethod(pivotIndex,leftOfPivotIndex -1);
return leftOfPivotIndex -1;
}
}
}
return -1;
}
private void mySwapMethod(int leftIndex,int rightIndex) {
int temp = array[leftIndex];
array[leftIndex] = array[rightIndex];
array[rightIndex] = temp;
}
}
【问题讨论】：
-
StackOverflowError表示堆栈溢出，很可能是无限递归造成的。 -
这里没有专家，但是如果您将
if(indexStart == indexEnd) {更改为if(indexStart >= indexEnd) {会发生什么？但是，是的，你在这个方法中递归（你可能已经知道了），但是你的递归不会在堆栈内存用完之前结束。 -
装满鳗鱼的气垫船，确实解决了问题！太感谢了！您认为您能够向我确切解释为什么将 if(indexStart == indexEnd) { 更改为 if(indexStart >= indexEnd) 可以解决问题以及导致问题的原因？再次感谢您！
-
其实没关系，我明白为什么现在可以修复它了。再次感谢充满鳗鱼的气垫船！感谢您的帮助。
标签： java algorithm sorting recursion quicksort