POJ 1251 解题报告

/*
ID: thestor1
LANG: C++
TASK: poj1251
*/
#include <iostream>
#include <fstream>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <limits>
#include <string>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <algorithm>
#include <cassert>

using namespace std;

void makeset(const int N, std::vector<int> &parent, std::vector<int> &rank)
{
for (int u = 0; u < N; ++u)
{
parent[u] = u;
rank[u] = 0;
}
}

int find(int u, std::vector<int> &parent)
{
if (parent[u] != u)
{
parent[u] = find(parent[u], parent);
}
return parent[u];
}

void union_set(int u, int v, std::vector<int> &parent, std::vector<int> &rank)
{
int ru = find(u, parent);
int rv = find(v, parent);
if (ru == rv)
{
return;
}

if (rank[ru] < rank[rv])
{
parent[ru] = rv;
}
else if (rank[rv] < rank[ru])
{
parent[rv] = ru;
}
else
{
parent[ru] = rv;
rank[rv]++;
}
}

class Edge
{
public:
int u, v, w;
Edge() {}
Edge(int u, int v, int w) : u(u), v(v), w(w) {}

bool operator< (const Edge &rhs) const
{
if (this->w != rhs.w)
{
return this->w < rhs.w;
}
return this->u < rhs.u || (this->u == rhs.u && this->v < rhs.v);
}
};

int kruskal(const int N, std::vector<Edge> &edges)
{
std::vector<int> parent(N);
std::vector<int> rank(N);

makeset(N, parent, rank);

sort(edges.begin(), edges.end());

int mst = 0;
for (int i = 0; i < edges.size(); ++i)
{
Edge edge = edges[i];
if (find(edge.u, parent) != find(edge.v, parent))
{
mst += edge.w;
union_set(edge.u, edge.v, parent, rank);
}
}
return mst;
}

int main()
{
while (true)
{
int N;
scanf("%d", &N);
if (N == 0)
{
break;
}

std::vector<Edge> edges;
for (int u = 0; u < N - 1; ++u)
{
char c;
int n;
scanf(" %c %d", &c, &n);
assert (c == 'A' + u);
for (int i = 0; i < n; ++i)
{
int w;
scanf(" %c %d", &c, &w);
assert(c > 'A' + u && c < 'A' + N);
edges.push_back(Edge(u, c - 'A', w));
}
}

int mst = kruskal(N, edges);
printf("%d\n", mst);
}

return 0;
}