[HDU - 5253]连接的管道

克鲁斯卡尔（最小生成树）

#include <stdio.h>
#include <math.h>
#include <iostream>
#include <algorithm>
#include <math.h>
#include <stdlib.h>
#include <string.h>
using namespace std;
#define maxn 1005
int n, m;
int a[maxn][maxn];
int father[maxn * maxn];

struct Edge
{
    int u;
    int v;
    int w;
}edge[2 * maxn * maxn];
int Find(int x)
{
    return father[x] == x ? x : father[x] = Find(father[x]);
}
int cmp(Edge a,Edge b)
{
    return a.w < b.w;
}
int kruscal(int m)
{
    sort(edge + 1, edge + m, cmp);
    int ans = 0;
    for(int i = 1; i < m; i++)
    {
        int x = Find(edge[i].u);
        int y = Find(edge[i].v);
        if(x != y)
        {
            father[x] = y;
            ans += edge[i].w;
        }
    }
    return ans;
}
int main()
{
    int tcase;
    scanf("%d", &tcase);
    int t = 1;
    while (tcase--)
    {
        scanf("%d%d", &n, &m);
        for (int i = 0; i < n; i++)
        {
            for (int j = 0; j < m; j++)
            {
                father[i * m + j] = i * m + j;
                scanf("%d", &a[i][j]);
            }
        }
        int id = 1;
        for (int i = 0; i < n; i++)
        {
            for (int j = 0; j < m; j++)
            {
                int u = i * m + j;
                if (i > 0)
                {
                    int v = (i-1) * m + j;
                    edge[id].u = u;
                    edge[id].v = v;
                    edge[id++].w = abs(a[i][j] - a[i-1][j]);
                }
                if (j > 0)
                {
                    int v = i*m+j-1;
                    edge[id].u = u;
                    edge[id].v = v;
                    edge[id++].w = abs(a[i][j] - a[i][j-1]);
                }
            }
        }
        int ans = kruscal(id);
        printf("Case #%d:\n%d\n", t++, ans);
    }
}