我一直在尝试在UVa Judge Online上进行341 Non-Stop Travel Problem，但是当我提交我的代码时，法官说有一个运行时错误（RE），我无法检测到它。我使用Dijkstra算法和邻接列表图解决了这个问题。当我测试输入示例时，我的程序工作正常，但我不知道如何跳过此运行时错误！我的代码在下面
#include <iostream>
#include <vector>
#include <list>
#define INFINITY 9999999
#define NIL -1
using namespace std;
class Dijkstra;
class Arc;
class Vertex;
class Graph;
class Arc
{
public:
int src;
int dst;
int weight;
Arc (int _src, int _dst, int _weight)
{
src = _src;
dst = _dst;
weight = _weight;
}
~Arc ()
{
}
};
class Vertex
{
public:
vector<Arc*> arcs;
Vertex ()
{
arcs = vector<Arc*>();
}
~Vertex ()
{
for (int i = 0; i < (int) arcs.size(); i++)
{
delete arcs[i];
}
}
};
class Graph
{
public:
vector<Vertex*> vertices;
Graph()
{
vertices = vector<Vertex*>();
}
void addVertex ()
{
Vertex* v = new Vertex();
vertices.push_back(v);
}
void addArc(int _src, int _dst, int _weight)
{
Arc* a = new Arc(_src,_dst, _weight);
vertices[_src]->arcs.push_back(a);
}
int w(int u, int v)
{
for (int i = 0; i < (int) vertices[u]->arcs.size(); i++)
{
if (vertices[u]->arcs[i]->dst == v)
{
return vertices[u]->arcs[i]->weight;
}
}
return INFINITY;
}
void printGraph()
{
for (int i = 0; i < (int) vertices.size(); i++)
{
for (int j = 0; j < (int) vertices[i]->arcs.size(); j++)
{
cout << i+1 << " " << vertices[i]->arcs[j]->dst+1 << " " << vertices[i]->arcs[j]->weight << "\t";
}
cout << endl;
}
}
~Graph ()
{
for (int i = 0; i < (int) vertices.size(); i++)
{
vertices[i]->~Vertex();
delete vertices[i];
}
}
};
class Dijkstra
{
public:
int* d;
int* pi;
list<int> Q;
Dijkstra()
{
}
void shortest_paths(Graph* G, int s)
{
initialize(G,s);
Q = addVertices(G);
while (Q.size() != 0)
{
int u = extractCheapest(Q);
Q.remove(u);
if (d[u] == INFINITY)
{
break;
}
for (int i = 0; i < (int) G->vertices[u]->arcs.size(); i++)
{
int v = G->vertices[u]->arcs[i]->dst;
relax(G,u,v);
}
}
}
void initialize(Graph* G, int s)
{
int size = G->vertices.size();
d = new int[size];
pi = new int[size];
for (int i = 0; i < size; i++)
{
d[i] = INFINITY;
pi[i] = NIL;
}
d[s] = 0;
}
void relax(Graph* G, int u, int v)
{
int w = (d[u] + G->w(u,v));
if (d[v] > w)
{
d[v] = w;
pi[v] = u;
}
}
list<int> addVertices(Graph* G)
{
list<int> q;
for (int i = 0; i < (int) G->vertices.size(); i++)
{
q.push_back(i);
}
return q;
}
int extractCheapest(list<int> Q)
{
int minorDist = INFINITY;
int minorVertex = NIL;
list<int>::iterator it;
for (it = Q.begin(); it != Q.end(); it++)
{
int dist = d[(*it)];
if ( dist < minorDist )
{
minorDist = dist;
minorVertex = (*it);
}
}
return minorVertex;
}
void printOutput (int cnt, int _d)
{
cout << "Case " << cnt << ": Path = ";
printRecursive(_d);
cout << "; ";
cout << d[_d] <<" second delay" << endl;
}
void printRecursive(int _d)
{
if(pi[_d] == NIL)
{
cout << " " << _d + 1;
}
else
{
printRecursive(pi[_d]);
cout << " "<< _d + 1;
}
}
~Dijkstra()
{
delete[] d;
delete[] pi;
}
};
int main ()
{
int NI;
int NE;
int weight;
int v;
int s;
int d;
int cnt = 0;
while (cin >> NI)
{
cnt++;
if (NI !=0 )
{
Graph* G = new Graph();
for (int u = 0; u < NI; u++)
{
G->addVertex();
cin >> NE;
for (int j = 0; j < NE; j++)
{
cin >> v;
cin >> weight;
G->addArc(u,v-1,weight);
}
}
cin >> s;
cin >> d;
Dijkstra* dijkstra = new Dijkstra();
dijkstra->shortest_paths(G,s-1);
dijkstra->printOutput(cnt,d-1);
G->~Graph();
dijkstra->~Dijkstra();
}
}
return 0;
}
------------------------------- EDIT --------------- --------------
我在代码中做了一些事情以避免运行时错误。首先，我纠正了内存泄漏的错误（感谢us2012和NPE！）然后我处理了断开连接图的情况。 This is the version of the code that was accepted by the judge.
答案 0 :(得分：0)
问题在于：
vertices[i]->~Vertex();
delete vertices[i];
析构函数会在delete时自动调用，所以基本上你会调用它两次。这就是你不知道的时候你会发现的:(标记为"HERE:"的相关行）
$ valgrind --tool=memcheck ./program341
==3954== Memcheck, a memory error detector
==3954== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==3954== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==3954== Command: ./program341
==3954==
5
2 3 3 4 6
3 1 2 3 7 5 6
1 4 5
0
1 4 7
2 4
Case 1: Path = 2 1 4; 8 second delay
==3954== Invalid read of size 4
==3954== at 0x8048F00: Vertex::~Vertex() (341.cc:48)
HERE: ==3954== by 0x8049155: Graph::~Graph() (341.cc:103)
==3954== by 0x8048D7C: main (341.cc:254)
==3954== Address 0x4336198 is 0 bytes inside a block of size 8 free'd
==3954== at 0x402AC1D: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==3954== by 0x804B1BA: __gnu_cxx::new_allocator<Arc*>::deallocate(Arc**, unsigned int) (new_allocator.h:100)
==3954== by 0x804A3DA: std::_Vector_base<Arc*, std::allocator<Arc*> >::_M_deallocate(Arc**, unsigned int) (stl_vector.h:175)
==3954== by 0x804A276: std::_Vector_base<Arc*, std::allocator<Arc*> >::~_Vector_base() (stl_vector.h:161)
==3954== by 0x8049779: std::vector<Arc*, std::allocator<Arc*> >::~vector() (stl_vector.h:404)
==3954== by 0x8048F3B: Vertex::~Vertex() (341.cc:45)
HERE: ==3954== by 0x8049135: Graph::~Graph() (341.cc:102)
==3954== by 0x8048D7C: main (341.cc:254)
...
...