PKU 1258 Agri-Net

　　　文章作者：ktyanny 文章来源：ktyanny 转载请注明，谢谢合作。   　　

 　　

　　话说N久没做题了，手生……今天拿一道很水的最小生成树来做，很水的。理解题意后一看就是赤裸裸的最小生成树算法题。好吧，二话不多说，贴上我的代码： 

　　

/*
by ktyanny
2010.01.26
C++ 47MS
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <iostream>
using namespace std;

const int MAX = 105;

typedef struct
{
    int a, b;
}point;

point v[MAX];

typedef struct
{
    int x, y;
    int w;
}edge;
const int MAXN = 50005;
edge e[MAXN];
int ans;

int rank[MAXN];
int pa[MAXN];

void make_set(int x)
{
    pa[x] = x;
    rank[x] = 0;
}

int find_set(int x)
{
    if(x != pa[x])
        pa[x] = find_set(pa[x]);
    return pa[x];
}

/*按秩合并x，y所在的集合*/
void union_set(int x, int y, int w)
{
    x = find_set(x);
    y = find_set(y);
    if(x == y)return ;
    ans += w;
    if(rank[x] > rank[y])/*让rank比较高的作为父结点*/
    {
        pa[y] = x;
    }
    else 
    {
        pa[x] = y;
        if(rank[x] == rank[y])
            rank[y]++;
    }
}


int cmp(const void *a, const void *b)
{
    return ( (*(edge *)a).w > (*(edge *)b).w ) ? 1 : -1;
}

int main()
{
    int n, i, j, jj, x, y, k, t;   
    while(cin >> n)
    {
        k = 0;
        ans = 0;
        for(i = 0; i < n; i++){
            for(j = 0; j < n; j++)
            {
                scanf("%d", &t);
                if(i < j){
                    e[k].w = t;
                    e[k].x = i;
                    e[k].y = j;
                    k++;
                }
            }
        }

        n = n * n;
        for(i = 0; i <= n; i++)
            make_set(i);

        qsort(e, k, sizeof(e[0]), cmp);

        /*Kruscal过程求最小生成树*/
        ans = 0;
        for(i = 0; i < k; i++)
        {
            x = find_set(e[i].x);
            y = find_set(e[i].y);
            if(x != y)
                union_set(x, y, e[i].w);
        }
        printf("%d\n", ans);
    }
    return 0;
}