最近我参加了有关数据结构的课程,我了解到QuickUnion在连接两个元素时的性能比QuickFind好。但是,当我在GCC中测试相同的代码时,Windows 10而不是Mac OS X,老师的机器,我得到了完全不同的运行时结果,但不知道为什么。这里是QuickFind的代码。在Windows和Mac OS中运行UnionFind时,为什么运行时存在很大差异?
#ifndef INC_03_QUICK_UNION_UNIONFIND1_H
#define INC_03_QUICK_UNION_UNIONFIND1_H
#include <cassert>
using namespace std;
namespace UF1 {
class UnionFind {
private:
int *id;
int count;
public:
UnionFind(int n) {
count = n;
id = new int[n];
for (int i = 0; i < n; i++)
id[i] = i;
}
~UnionFind() {
delete[] id;
}
int find(int p) {
assert(p >= 0 && p < count);
return id[p];
}
bool isConnected(int p, int q) {
return find(p) == find(q);
}
void unionElements(int p, int q) {
int pID = find(p);
int qID = find(q);
if (pID == qID)
return;
for (int i = 0; i < count; i++)
if (id[i] == pID)
id[i] = qID;
}
};
}
#endif //INC_03_QUICK_UNION_UNIONFIND1_H
而且QuickUnion:
#ifndef INC_03_QUICK_UNION_UNIONFIND2_H
#define INC_03_QUICK_UNION_UNIONFIND2_H
#include <cassert>
using namespace std;
namespace UF2{
class UnionFind{
private:
int* parent;
int count;
public:
UnionFind(int count){
parent = new int[count];
this->count = count;
for(int i = 0 ; i < count ; i ++)
parent[i] = i;
}
~UnionFind(){
delete[] parent;
}
int find(int p){
assert(p >= 0 && p < count);
while(p != parent[p])
p = parent[p];
return p;
}
bool isConnected(int p , int q){
return find(p) == find(q);
}
void unionElements(int p, int q){
int pRoot = find(p);
int qRoot = find(q);
if(pRoot == qRoot)
return;
parent[pRoot] = qRoot;
}
};
}
#endif //INC_03_QUICK_UNION_UNIONFIND2_H
然后UnionFindTestHelper,一类可以帮助测试两种数据结构:
#ifndef INC_03_QUICK_UNION_UNIONFINDTESTHELPER_H
#define INC_03_QUICK_UNION_UNIONFINDTESTHELPER_H
#include <iostream>
#include <ctime>
#include "UnionFind1.h"
#include "UnionFind2.h"
using namespace std;
namespace UnionFindTestHelper{
void testUF1(int n){
srand(time(NULL));
UF1::UnionFind uf = UF1::UnionFind(n);
time_t startTime = clock();
for(int i = 0 ; i < n ; i ++){
int a = rand()%n;
int b = rand()%n;
uf.unionElements(a,b);
}
for(int i = 0 ; i < n ; i ++){
int a = rand()%n;
int b = rand()%n;
uf.isConnected(a,b);
}
time_t endTime = clock();
cout<<"UF1, "<<2*n<<" ops, "<<double(endTime-startTime)/CLOCKS_PER_SEC<<" s"<<endl;
}
void testUF2(int n){
srand(time(NULL));
UF2::UnionFind uf = UF2::UnionFind(n);
time_t startTime = clock();
for(int i = 0 ; i < n ; i ++){
int a = rand()%n;
int b = rand()%n;
uf.unionElements(a,b);
}
for(int i = 0 ; i < n ; i ++){
int a = rand()%n;
int b = rand()%n;
uf.isConnected(a,b);
}
time_t endTime = clock();
cout<<"UF2, "<<2*n<<" ops, "<<double(endTime-startTime)/CLOCKS_PER_SEC<<" s"<<endl;
}
}
#endif //INC_03_QUICK_UNION_UNIONFINDTESTHELPER_H
最后的main.cpp:
#include <iostream>
#include "UnionFindTestHelper.h"
using namespace std;
int main() {
int n = 100000;
UnionFindTestHelper::testUF1(n);
UnionFindTestHelper::testUF2(n);
return 0;
}
老师测试了Qu ckUnion可以比QuickFind节省一半的时间,但是当我在Windows 10 x64中测试时,两个运行时结果几乎相同。我不知道我是否犯了错误或操作系统的差异导致。