买礼物

Posted 2020-10-12

 原题链接：https://www.luogu.org/problem/show?pid=1194#sub

日常数组开小（1/1）。

一个裸的最小生成树。跑一遍最小生成树记录一下所花价钱，然后扫一下father数组把没优惠的补上，输出就好了。

参考代码：

 1 #include <iostream>
 2 #include <cstring>
 3 #include <cstdio>
 4 #include <algorithm>
 5 #define maxn 500000
 6 using namespace std;
 7 struct Edge{
 8     int from,to,dis;
 9     bool operator<(const Edge &rhs)const{
10         return dis < rhs.dis;
11     }
12 };
13 inline int read(){
14     int num = 0;
15     char c;
16     bool flag = false;
17     while ((c = getchar()) == ‘ ‘ || c == ‘\n‘ || c == ‘\r‘);
18     if (c == ‘-‘)
19         flag = true;
20     else
21         num = c - ‘0‘;
22     while (isdigit(c = getchar()))
23         num = num * 10 + c - ‘0‘;
24     return (flag ? -1 : 1) * num;
25 }
26 Edge edge[maxn];
27 int father[maxn];
28 int n,m;
29 int tot = 0;
30 int ans,totedge,readnum;
31 int find(int x){
32     if (father[x] == x)
33         return father[x];
34     else
35         return find(father[x]);
36 }
37 void merge(int x,int y){
38     father[find(y)] = find(x);
39 }
40 bool check(int x,int y){
41     return find(x) == find(y);
42 }
43 int main(){
44     n = read();m = read();
45     for (register int i=1;i<=m;i++)
46         father[i] = i;
47     for (register int i=1;i<=m;i++)
48         for (register int j=1;j<=m;j++){
49             readnum = read();
50             if (readnum!=0){
51                 edge[++tot].from = i;
52                 edge[tot].to = j;
53                 edge[tot].dis = readnum;
54             }
55         }
56     sort(edge+1,edge+tot+1);
57     for (register int i=1;i<=tot;i++){
58         int u = edge[i].from;
59         int v = edge[i].to;
60         if (!check(u,v)){
61             totedge++;
62             ans += edge[i].dis;
63             merge(u,v);
64             if (totedge == m-1)
65                 break;
66         }
67     }
68     for (register int i=1;i<=n;i++)
69         if (father[i] == i)
70             ans += n;
71     printf("%d\n",ans);
72     return 0;
73 }