luogu P1455 搭配购买 题解

Posted 2020-10-29 Misaka_Azusa

题目链接：https://www.luogu.org/problemnew/show/P1455

一句话题目做法：并查集合并+01背包

启示：要每次再find一遍。路径压缩会快。因为合并的时候如果是1连3,3连2,4连2，最后也不能保证一步就能连到fa上去。

结果会是fa[2] = fa[3] = fa[4] = 2.

　　　　fa[1] = 3.

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <algorithm>
 4 using namespace std;
 5 const int maxn = 10010;
 6 int n,m,money,fa[maxn];//n朵云,m个搭配,w现有钱的数目 
 7 int qwqw[maxn],f[maxn],qwqc[maxn],w[maxn],c[maxn];
 8 int find(int x)
 9 {
10     return x==fa[x]?x:fa[x]=find(fa[x]);
11 } 
12 int unionn(int x, int y)
13 {
14 
15 }
16 int main()
17 {    
18     scanf("%d%d%d",&n,&m,&money);
19     
20     for(int i = 1; i <= n; i++)
21     fa[i] = i;
22     
23     for(int i = 1; i <= n; i++)
24     {
25         int fee,d;
26         scanf("%d%d",&fee,&d);
27         w[i] = fee; c[i] = d;
28     }
29     for(int i = 1; i <= m; i++)
30     {
31         int u,v;
32         scanf("%d%d",&u,&v);
33         int x = find(u);
34         int y = find(v);
35         if(x!=y)
36         fa[y] = x;
37     }
38 
39     for(int i = 1; i <= n; i++)
40     {
41         if(fa[i]!=i)
42         {
43             c[find(i)] += c[i];
44             w[find(i)] += w[i];
45             c[i] = 0; w[i] = 0;
46         }
47     }
48     
49     for(int i = 1; i <= n; i++)
50         for(int v = money; v >= w[i]; v--)
51         f[v] = max(f[v],f[v-w[i]]+c[i]);
52     printf("%d",f[money]);
53     return 0;
54 }