Giúp đỡ về quicksort trong <vector>string

[Nguy_n_Anh_Ki_t (Nguyễn Anh Kiệt)]

Mọi người ơi, em code như thế này mò mãi sao chả ra được lỗi, sau khi chạy quicksort mảng vẫn giữ nguyên như cũ, mọi người giúp em với

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
void Hoanvi (string *a, string *b);
void quickSort(vector<string> a, int low, int high);
int partition (vector<string> a, int low, int high);
int compare( string s1, string s2);

// void quickSort( vector<string> &a, int low, int high)
void main()
{
	//Khai bao bien
	fstream f;
	vector <string> danhsach;

	// Xu ly file:  string str(a) bien a thanh string  
	//Input
	f.open("Input.txt",ios::in);
	int count = 0;
	f >> count;
	danhsach.resize(count);
	string tam;
	getline(f,tam);
	for (int i = 0; i < count; i++)
	{
		getline(f,danhsach[i]);a
	}
	f.close();


	// Xu ly mang:
	quickSort(danhsach,0,count-1);


	//Output
	fstream o;
	o.open("Output.txt",ios::out);
	for (int i = 0; i < count; i++)
		o << danhsach[i] << endl;
	o.close();
	
}

void quickSort(vector<string> a, int low, int high)
{
	if (low < high)
	{
		int p = partition(a,low,high);	
		quickSort (a, low, p-1);
		quickSort (a,p+1,high);

	}
}
void Hoanvi (string *a, string *b)
{
	string tam = *a;
	*a = *b;
	*b = tam;
}
int partition (vector<string> a, int low, int high)
{
	string pivot = a[(low+high)/2]; // thay int = string
	int i = low;
	int j = high;
	
	while (i < j )
	{
		//// s1 < s2 ==> <0
		//// s1 > s2 ==> >0
		//// s1 = s2 ==> 0 
		//while (compare(a[i],pivot) < 0 )
		//	i++;				
		//while (compare(a[j],pivot) > 0 )				
		//	j--	;			// chinh sua 
		//if ( i < j )
		//{
		//	Hoanvi(&(string)a[i],&(string)a[j]);
		//	//a[i].swap(a[j]);
		//	/*cout << "Truoc khi xep: \n";
		//	cout << "\na[i]: " << a[i] << endl;
		//	cout << "\na[j]: " << a[j] << endl;
		//	swap((a[i]),(a[j]));
		//	cout << "Sau khi xep: \n";
		//	cout << "\na[i]: " << a[i] << endl;
		//	cout << "\na[j]: " << a[j] << endl;*/
		//	i++;
		//	j--;
		//}	
		while (compare(a[i],pivot) > 0 ) 
			i++;
		while (compare(a[j],pivot) < 0)
			j--;
		if ( i < j)
		{
			Hoanvi(&a[i],&a[j]);
			//a[i].swap(a[j]);
			i++;
			j--;
		}
	}
	return j;
}

int compare( string s1, string s2)
{
	char *t1;
	t1 = &s1[0];
	t1 = strlwr(t1);
	


	char *t2;
	t2 = &s2[0];
	t2 = strlwr(t2);
	
	

	char* t1_lwr = strlwr(t1);
	char* t2_lwr = strlwr(t2);
	return strcmp(t1_lwr,t2_lwr);
	// s1 < s2 ==> <0
	// s1 > s2 ==> >0
	// s1 = s2 ==> 0 
}


// char*  t1 = strdup (s1.c_str());  chuyen thanh chu thuong:	strlwn(t1)

[Gio (Gió)]

Qsort(vector< string> &a…)
partition(vector< string> & a…)