C ++快速排序字符串文本 [英] c++ quicksort sort string text
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问题描述
我正在做作业,并且完成了递归快速排序,但是排序方式不正确。
I am doing my homework, and completed quicksort recursive, however it doesn't sort in a correct way. Seems to be it doesn't swap correctly.
这是我的代码
#include<iostream>
#include<ctime>
#include<string>
using namespace std;
int quick_sort_help(string &text,int left, int right, int pivot){
char val = text[pivot];
char temp;
//swap
// temp =text[pivot];
//text[pivot]= text[right];
//text[right]=temp;
//swap(&text[left],&text[right]);
int l = left;
int r = right;
int i=left;
while (i<=r)
{
while (text[i]<val)
i++;
while (text[right]>val)
r--;
if (i<=r)
{
temp=text[i];
text[i]=text[r];
text[r]=temp;
i++;
r--;
}
}
return l;
}
void quicksort(string &text,int left, int right){
if (left < right){
int pivot=(left+right)/2;
int pivottwo = quick_sort_help(text, left, right, pivot);
quicksort(text, left, pivottwo - 1);
quicksort(text, pivottwo + 1, right);
}
}
void quick_sort(string &text,int size){
quicksort(text,0,size);}
int main()
{
string text="this is a test string text,.,!";
int size = text.length();
float t1, t2;
t1 = clock();
quick_sort(text,size);
t2=clock();
cout<<"quicksort Sort: "<<(t2-t1)/CLK_TCK*1000<<" msec\n";
cout<<text<<endl;
system("pause");
return 0;
}
我得到的输出:
hi a e e,g.nii,r!tssssxttttt
推荐答案
您必须:
1)不要使用大小,而是使用大小为1的值
1) Don't use size but size-1 value
void quick_sort(string &text,int size){
quicksort(text,0,size-1);}
2)Pivot不是(left + right)/ 2,但这是quick_sort_help返回的值,pivottwo不是必需的:
2) Pivot is not (left+right)/2 but it's the value returned by quick_sort_help, and pivottwo is not necessary:
void quicksort(string &text,int left, int right)
{
if (left < right)
{
int pivot = quick_sort_help(text, left, right);
quicksort(text, left, pivot - 1);
quicksort(text, pivot + 1, right);
}
}
3)测试我的j值(您的r)第二次,然后在返回支点(i值)之前进行交换:
3) Test my j value (your r) in the second while and make the exchange before returning the pivot (the i value):
int quick_sort_help(string &text,int left, int right)
{
char val = text[right];
char temp;
int j = right;
int i = left - 1;
while (true)
{
while (text[++i] < val);
while (text[--j] > val) {
if(j == left)
break;
}
if(i >= j)
break;
temp=text[i];
text[i]=text[j];
text[j]=temp;
}
temp=text[i];
text[i]=text[right];
text[right]=temp;
return i;
}
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