我有这个用于 Prim Algo 的 MST 实现,它是 |V| 到电源 3。但是 CLRS 说它说复杂度是 O (E * lg |V| ) 假设 |V| ~ |E| 它的 O(|V| * lg |V|) 。我的实现可能是固定的,但我不确定我们如何才能低于 |V| * |V| 用矩阵实现
class matrix_graph
{
private:
int** v;
int vertexes;
public:
matrix_graph(int**, int);
~matrix_graph(void);
bool is_connected(int i,int j);
int egde_weight(int i,int j){return v[i][j];}
};
int mst()
{
int v[9][9] = {
{0,4,0,0,0,0,0,0,8},
{0,0,8,0,0,0,0,0,11},
{0,8,0,7,0,4,0,2,0},
{0,0,7,0,9,14,0,0,0},
{0,0,0,9,0,10,0,0,0},
{0,0,4,14,10,0,2,0,0},
{0,0,0,0,0,2,0,6,1},
{0,0,2,0,0,0,6,0,7},
{8,11,0,0,0,0,1,7,0}
};
int* ptr_v[9];
for(int i=0;i<9;i++){
ptr_v[i] = & v[i][0];
}
matrix_graph* m = new matrix_graph(ptr_v , 9 );
std::set<int> tree;
tree.insert(0);
std::set<int> non_tree;
non_tree.insert(1);
non_tree.insert(2);
non_tree.insert(3);
non_tree.insert(4);
non_tree.insert(5);
non_tree.insert(6);
non_tree.insert(7);
non_tree.insert(8);
int i = 0;
int min = _I32_MAX;
int add_to_tree;
int sum = 0;
while(!non_tree.empty()){
for(std::set<int>::iterator iter = tree.begin() ; iter != tree.end() ; iter++ ){
for(std::set<int>::iterator iter_n = non_tree.begin() ; iter_n != non_tree.end() ; iter_n++){
int edge = m->egde_weight(*iter , *iter_n);
if( edge > 0 && edge < min)
{
min = edge;
add_to_tree = *iter_n;
}
}
}
tree.insert(add_to_tree);
non_tree.erase(add_to_tree);
sum += min;
min = _I32_MAX;
}
return sum;
}