luogu P2170 选学霸

传送门

比较简单的题

并查集维护一下必须选择的大小 也就是物品

然后0/1背包处理指定体积能否组成

(一开始开bool想做一个传递真值就是D不出来....能有dalao讲一下吗)

Code:

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#define ms(a,b) memset(a,b,sizeof a)
#define rep(i,a,n) for(int i = a;i <= n;i++)
#define per(i,n,a) for(int i = n;i >= a;i--)
#define inf 1000000007
using namespace std;
typedef long long ll;
typedef double D;
#define eps 1e-8
ll read() {
    ll as = 0,fu = 1;
    char c = getchar();
    while(c < '0' || c > '9') {
        if(c == '-') fu = -1;
        c = getchar();
    }
    while(c >= '0' && c <= '9') {
        as = as * 10 + c - '0';
        c = getchar();
    }
    return as * fu;
}
//head
const int N = 100005;
int n,m,k;

int pa[N],d[N];
int gpa(int x) {
    if(pa[x] == x) return x;
    return pa[x] = gpa(pa[x]);
}
int Merge(int x,int y) {
    int fx = gpa(x),fy = gpa(y);
    if(fx ^ fy) pa[fx] = fy,d[fy] += d[fx];
}

int stk[N],top;
int dp[N<<1];
#define Abs(x) (((x)>(~(x)+1)) ? x : (~(x)+1))
int main() {
    // freopen("in.in","r",stdin);
    n = read(),m = read(),k = read();
    rep(i,1,n) pa[i] = i,d[i] = 1;
    rep(i,1,k) Merge(read(),read());
    rep(i,1,n) if(pa[i] == i) stk[++top] = d[i];
    rep(i,1,top) {
        per(j,m<<1,stk[i]) {
            dp[j] = max(dp[j],dp[j-stk[i]] + stk[i]);
        }
    }
    int ans = inf,minn = inf;
    rep(i,1,m<<1) {
        if(minn > Abs(dp[i]-m)) minn = Abs(dp[i]-m),ans = dp[i];
    }
    printf("%d
",ans == inf ? 0 : ans);
    return 0;
}