2020牛客寒假算法基础集训营1

F.maki和tree

题解：
满足题意的两种组合，第一种是一端为白色，另一端为黑色，第二种是两端都为白，遍历字符串，枚举黑色的节点，dfs搜索与该节点的白色节点数。设某黑点连接了 k 个白点，第 i 个白点的权值为 f(i) 。两种数量分别是：

AC_CODE：

/*
 * Author: $%U%$
 * Time: $%Y%$-$%M%$-$%D%$ $%h%$:$%m%$:$%s%$
*/
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<string>
#include<iostream>
#include<sstream>
#include<set>
#include<map>
#include<queue>
#include<bitset>
#include<vector>
#include<limits.h>
#include<assert.h>
#define SZ(X) ((int)(X).size())
#define ALL(X) (X).begin(), (X).end()
#define REP(I, N) for (int I = 0; I < (N); ++I)
#define REPP(I, A, B) for (int I = (A); I < (B); ++I)
#define FOR(I, A, B) for (int I = (A); I <= (B); ++I)
#define FORS(I, S) for (int I = 0; S[I]; ++I)
#define RS(X) scanf("%s", (X))
#define SORT_UNIQUE(c) (sort(c.begin(),c.end()), c.resize(distance(c.begin(),unique(c.begin(),c.end()))))
#define GET_POS(c,x) (lower_bound(c.begin(),c.end(),x)-c.begin())
#define CASET int ___T; scanf("%d", &___T); for(int cs=1;cs<=___T;cs++)
#define MP make_pair
#define PB push_back
#define MS0(X) memset((X), 0, sizeof((X)))
#define MS1(X) memset((X), -1, sizeof((X)))
#define LEN(X) strlen(X)
#define F first
#define S second
using namespace std;
typedef long long ll,LL;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int,int> PII;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef vector<PII> VPII;
typedef pair<LL,LL> PLL;
typedef vector<PLL> VPLL;
template<class T> void _R(T &x) { cin >> x; }
void _R(int &x) { scanf("%d", &x); }
void _R(LL &x) { scanf("%lld", &x); }
void _R(double &x) { scanf("%lf", &x); }
void _R(char &x) { scanf(" %c", &x); }
void _R(char *x) { scanf("%s", x); }
void R() {}
template<class T, class... U> void R(T &head, U &... tail) { _R(head); R(tail...); }
template<class T> void _W(const T &x) { cout << x; }
void _W(const int &x) { printf("%d", x); }
void _W(const LL &x) { printf("%lld", x); }
void _W(const double &x) { printf("%.16f", x); }
void _W(const char &x) { putchar(x); }
void _W(const char *x) { printf("%s", x); }
template<class T,class U> void _W(const pair<T,U> &x) {_W(x.F); putchar(' '); _W(x.S);}
template<class T> void _W(const vector<T> &x) { for (auto i = x.begin(); i != x.end(); _W(*i++)) if (i != x.cbegin()) putchar(' '); }
void W() {}
template<class T, class... U> void W(const T &head, const U &... tail) { _W(head); putchar(sizeof...(tail) ? ' ' : '\n'); W(tail...); }
#ifdef HOME
 #define DEBUG(...) {printf("# ");printf(__VA_ARGS__);puts("");}
#else
 #define DEBUG(...)
#endif
#define in freopen("in.txt","r",stdin);
#define out freopen("out.txt","w",stdout);
#define mod 998244353
ll powmod(ll a,ll b) {ll res=1;a%=mod; assert(b>=0); for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
const int maxn = 1e5+5;
char s[maxn];
int n;
VI v[maxn];
bool vis[maxn];
ll cnt;

void dfs(int x){
    REPP(i,0,SZ(v[x])){
        int j = v[x][i];
        if(!vis[j] && s[j] == 'W') {
            vis[j] = 1;
            dfs(j);
            cnt += 1;
        }
    }
}

ll count(int x){
    ll res = 0, tot = 0;
    MS0(vis);
    REPP(i,0,SZ(v[x])){
        int j = v[x][i];
        if(s[j] == 'B' || vis[j]) continue;
        cnt = 1;
        vis[j] = 1;
        dfs(j);
        res += tot * cnt + cnt;
        tot += cnt;
    }
    return res;
}

int main(){
    R(n);
    scanf("%s",s+1);
    REPP(i,1,n){
        int x,y;
        R(x,y);
        v[x].PB(y);
        v[y].PB(x);
    }
    ll sum = 0LL;
    FOR(i,1,n){
        if(s[i] == 'B'){
            sum += count(i);
        }
    }
    W(sum);
}

umi和弓道

题解：
记录线段在坐标轴的交点，x轴和y轴分开计算，维护n-k个数即可。

AC_CODE:

/*
 * Author: $%U%$
 * Time: $%Y%$-$%M%$-$%D%$ $%h%$:$%m%$:$%s%$
*/
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<string>
#include<iostream>
#include<sstream>
#include<set>
#include<map>
#include<queue>
#include<bitset>
#include<vector>
#include<limits.h>
#include<assert.h>
#define SZ(X) ((int)(X).size())
#define ALL(X) (X).begin(), (X).end()
#define REP(I, N) for (int I = 0; I < (N); ++I)
#define REPP(I, A, B) for (int I = (A); I < (B); ++I)
#define FOR(I, A, B) for (int I = (A); I <= (B); ++I)
#define FORS(I, S) for (int I = 0; S[I]; ++I)
#define RS(X) scanf("%s", (X))
#define SORT_UNIQUE(c) (sort(c.begin(),c.end()), c.resize(distance(c.begin(),unique(c.begin(),c.end()))))
#define GET_POS(c,x) (lower_bound(c.begin(),c.end(),x)-c.begin())
#define CASET int ___T; scanf("%d", &___T); for(int cs=1;cs<=___T;cs++)
#define MP make_pair
#define PB push_back
#define MS0(X) memset((X), 0, sizeof((X)))
#define MS1(X) memset((X), -1, sizeof((X)))
#define LEN(X) strlen(X)
#define F first
#define S second
using namespace std;
typedef long long ll,LL;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int,int> PII;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef vector<PII> VPII;
typedef pair<LL,LL> PLL;
typedef vector<PLL> VPLL;
template<class T> void _R(T &x) { cin >> x; }
void _R(int &x) { scanf("%d", &x); }
void _R(LL &x) { scanf("%lld", &x); }
void _R(double &x) { scanf("%lf", &x); }
void _R(char &x) { scanf(" %c", &x); }
void _R(char *x) { scanf("%s", x); }
void R() {}
template<class T, class... U> void R(T &head, U &... tail) { _R(head); R(tail...); }
template<class T> void _W(const T &x) { cout << x; }
void _W(const int &x) { printf("%d", x); }
void _W(const LL &x) { printf("%lld", x); }
void _W(const double &x) { printf("%.16f", x); }
void _W(const char &x) { putchar(x); }
void _W(const char *x) { printf("%s", x); }
template<class T,class U> void _W(const pair<T,U> &x) {_W(x.F); putchar(' '); _W(x.S);}
template<class T> void _W(const vector<T> &x) { for (auto i = x.begin(); i != x.end(); _W(*i++)) if (i != x.cbegin()) putchar(' '); }
void W() {}
template<class T, class... U> void W(const T &head, const U &... tail) { _W(head); putchar(sizeof...(tail) ? ' ' : '\n'); W(tail...); }
#ifdef HOME
 #define DEBUG(...) {printf("# ");printf(__VA_ARGS__);puts("");}
#else
 #define DEBUG(...)
#endif
#define in freopen("in.txt","r",stdin);
#define out freopen("out.txt","w",stdout);
#define mod 998244353
ll powmod(ll a,ll b) {ll res=1;a%=mod; assert(b>=0); for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
const int maxn = 4e6+5;
char s[maxn];
vector<double>v1,v2;

/*
struct node{
	
}k[maxn];
*/

int main(){
    double x0,y0;
    int n,k;
    R(x0,y0,n,k);
    k = n - k;
    FOR(i,1,n){
        double x,y;
        R(x,y);
        if(x*x0 < 0){
            v2.PB(y0-(y0-y)/(x0-x)*x0);
        }
        if(y*y0 < 0){
            v1.PB(x0-(x0-x)/(y0-y)*y0);
        }
    }
    double minn = 1LL<<62LL;
    sort(v1.begin(),v1.end());
    sort(v2.begin(),v2.end());
    REPP(i,0,SZ(v1)-k+1){
        minn = min(minn, v1[i+k-1]-v1[i]);
    }
    REPP(i,0,SZ(v2)-k+1){
        minn = min(minn, v2[i+k-1]-v2[i]);
    }
    if(minn == 1LL<<62LL) W(-1);
    else printf("%.8f\n",minn);
}