POJ 2421 Constructing Roads (最小生成树)

#include <iostream>
#include <cstdio>
#include <string>
#include <queue>
#include <vector>
#include <map>
#include <algorithm>
#include <cstring>
#include <cctype>
#include <cstdlib>
#include <cmath>
#include <ctime>
using    namespace    std;

const    int    SIZE = 105;
int    N,M,NUM;
int    FATHER[SIZE];
struct    Node
{
    int    from,to,cost;
}G[SIZE * SIZE];

void    ini(void);
int    find_father(int);
void    unite(int,int);
bool    same(int,int);
bool    comp(const Node &,const Node &);
int    kruskal(void);
int    main(void)
{
    int    from,to,cost;

    while(scanf("%d",&N) != EOF)
    {
        ini();
        for(int i = 1;i <= N;i ++)
            for(int j = 1;j <= N;j ++)
            {
                scanf("%d",&cost);
                if(i == j)
                    continue;
                if(i < j)
                {
                    G[NUM].from = i;
                    G[NUM].to = j;
                    G[NUM].cost = cost;
                    NUM ++;
                }
            }
        scanf("%d",&M);
        while(M --)
        {
            scanf("%d%d",&from,&to);
            unite(from,to);
        }
        sort(G,G + NUM,comp);
        printf("%d\n",kruskal());
    }

    return    0;
}

void    ini(void)
{
    NUM = 0;
    for(int i = 1;i <= N;i ++)
        FATHER[i] = i;
}

int    find_father(int n)
{
    if(n == FATHER[n])
        return    n;
    return    FATHER[n] = find_father(FATHER[n]);
}

void    unite(int x,int y)
{
    x = find_father(x);
    y = find_father(y);

    if(x == y)
        return    ;
    FATHER[x] = y;
}

bool    same(int x,int y)
{
    return    find_father(x) == find_father(y);
}

bool    comp(const Node & a,const Node & b)
{
    return    a.cost < b.cost;
}

int    kruskal(void)
{
    int    ans = 0,count = 0;

    for(int i = 0;i < NUM;i ++)
        if(!same(G[i].from,G[i].to))
        {
            unite(G[i].from,G[i].to);
            ans += G[i].cost;
            count ++;
            if(count == N - 1)
                break;
        }
    return    ans;
}