我有一个快速排序程序,工作伟大,直到我尝试排序具有重复数字的数组。程序陷入无限循环。我相信这发生在 While(lower< upper)代码块中。
code> void quickSort(int array [],int size){ if(size< 2)return; int pivot,lower,upper,temp; //设置第一个和最后一个元素的缩进 lower = 0; upper = size - 1; //随机选择枢轴元素 pivot = array [rand()%(size)]; while(lower< upper){ // Lower必须是数字<而不是一个数字> = pivot while(array [lower]< pivot){ lower ++; } while(array [upper]> pivot){ upper--; } //上下交换 temp = array [lower]; array [lower] = array [upper]; array [upper] = temp; } //递归地对数组的两个分区重复过去的操作 quickSort(array,lower); quickSort(& array [lower + 1],size-lower-1); }解决方案
/ p>
从维基百科,就地快速排序的伪代码如下: (不是说他们应该盲目信任)
function quicksort(array)如果length(array)> 1 pivot:=选择数组中的任何元素 left:=数组的第一个索引 right:=数组的最后一个索引 while left right right while array [左] pivot left:= left + 1 while array [right]> pivot right:= right - 1 如果left≤right swap数组[left] with数组[right] left:= left + 1 right: right-1 quicksort(从第一个索引到右侧的数组) quicksort(数组从左到上索引)因此,您看到它与您的算法非常相似,只需稍加修改。
while < = upper){此外,只有当
您的代码在递归调用中有所不同:
quicksort(数组从第一个索引到右侧){array [0]到array [upper]} quicksort这是因为现在它已经退出while循环了,因为它已经退出了一个循环。 #include< iostream> #include< cstdlib> using namespace std; void quickSort(int array [],int size){ if(size< 2)return; int pivot,lower,upper,temp; //设置第一个和最后一个元素的缩进 lower = 0; upper = size - 1; //随机选择枢轴元素 pivot = array [rand()%(size)]; while(lower< = upper){ // Lower必须是数字<而不是一个数字> = pivot while(array [lower]< pivot){ lower ++; } while(array [upper]> pivot){ upper--; } //交换上下 if(lower< = upper){ temp = array [lower]; array [lower] = array [upper]; array [upper] = temp; lower ++; upper--; } } //递归地对数组的两个分区重复过去的操作 quickSort(array,upper + 1); quickSort(& array [lower],size-lower); } int main(){ //你的代码在这里 int myArray [] = {10,9,8,7,7,7, 7,3,2,1}; quickSort(myArray,10); for(int i = 0; i <10; i ++) cout< myArray [i]< ; return 0; }输出:
1 2 3 7 7 7 7 8 9 10
I have a quicksort program that works great until I try to sort an array that has a repeating number. The program gets stuck in an infinite loop. I believe this is happening in the While(lower < upper) block of code.
void quickSort(int array[], int size){ if(size < 2) return; int pivot, lower, upper, temp; //Set the indeces for the first and last elements lower = 0; upper = size - 1; //Select pivot element randomly pivot = array[rand() % (size)]; while(lower < upper){ //Lower must be a number < than pivot and upper a number >= pivot while(array[lower] < pivot){ lower++; } while(array[upper] > pivot){ upper--; } //Swap upper and lower temp = array[lower]; array[lower] = array[upper]; array[upper] = temp; } //Repeat the past actions on the two partitions of the array recursively quickSort(array, lower); quickSort(&array[lower+1], size-lower-1); }解决方案
EDIT: Code added.
From Wikipedia, the pseudo-code for in-place quicksort is as follows: (Not saying that they should be trusted blindly)
function quicksort(array) if length(array) > 1 pivot := select any element of array left := first index of array right := last index of array while left ≤ right while array[left] < pivot left := left + 1 while array[right] > pivot right := right - 1 if left ≤ right swap array[left] with array[right] left := left + 1 right := right - 1 quicksort(array from first index to right) quicksort(array from left to last index)So you see it is quite similar to your algorithm, with minor modifications.
while(lower <= upper){Also you need to swap only if lower <= upper and then update the indices.
And your code differs in the recursive calls:
quicksort(array from first index to right) {array[0] to array[upper]} quicksort(array from left to last index) {array[lower] to array[size-1]}This is because now that it has exited the while loop, upper is less than lower.
Full working code:
#include <iostream> #include <cstdlib> using namespace std; void quickSort(int array[], int size){ if(size < 2) return; int pivot, lower, upper, temp; //Set the indeces for the first and last elements lower = 0; upper = size - 1; //Select pivot element randomly pivot = array[rand() % (size)]; while(lower <= upper){ //Lower must be a number < than pivot and upper a number >= pivot while(array[lower] < pivot){ lower++; } while(array[upper] > pivot){ upper--; } //Swap upper and lower if ( lower <= upper ) { temp = array[lower]; array[lower] = array[upper]; array[upper] = temp; lower++; upper--; } } //Repeat the past actions on the two partitions of the array recursively quickSort(array, upper+1); quickSort(&array[lower], size-lower); } int main() { // your code goes here int myArray[] = { 10, 9, 8, 7, 7, 7, 7, 3, 2, 1}; quickSort( myArray, 10 ); for ( int i = 0; i < 10; i++ ) cout << myArray[i] << " "; return 0; }Output:
1 2 3 7 7 7 7 8 9 10
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如果有重复值,则快速排序无限循环
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