A B

4801: 打牌

分类讨论就行了

比赛时一开始写挂了...

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;
typedef long long ll;
const int N = (1<<18) + 5;
inline int read(){
	char c=getchar();int x=0,f=1;
	while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}
	while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}
	return x*f;
}

int aq, bq, at, bt, c[300];
char s[5];
inline int f(int x) {return x==100 ? 1 : x;}

int solve(int a, int b, int c, int d) {
	//printf("solve %d %d  %d %d
", a, b, c, d);
	int ans = 0;
	if(a >= c) {
		ans += f(a);
		int t = 0;
		if(c > b) t = max(t, f(c));
		if(d > b) t = max(t, f(d));
		if(!t) ans += f(b);
		else ans -= t;
	} else {
		int t = 0;
		if(b < d || (b == d && a == b)) ans = -f(c) - f(d);
		else {
			t = min(f(a), f(b));
			ans = t - f(c);
		} 
	}
	return ans;
}
int main() {
	freopen("in", "r", stdin);
	int T = read();
	for(int i=1; i<=9; i++) c[i + '0'] = i; 
	c['T'] = 10; c['J'] = 11; c['Q'] = 12; c['K'] = 13; c['A'] = 100;
	while(T--) {
		int x, y;
		scanf("%s", s); x = c[ s[0] ];
		scanf("%s", s); y = c[ s[0] ];
		aq = max(x, y); bq = min(x, y);

		scanf("%s", s); x = c[ s[0] ];
		scanf("%s", s); y = c[ s[0] ];
		at = max(x, y); bt = min(x, y);
		
		printf("%d
", solve(aq, bq, at, bt));
	}
}

4832: 抵制克苏恩

裸期望DP，(f[i][a][b][c])

然而比赛的时候概率忘记乘上a,b,c的个数一直WA,我二轮药丸....

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;
typedef long long ll;
const int N = (1<<18) + 5;
inline int read(){
	char c=getchar();int x=0,f=1;
	while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}
	while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}
	return x*f;
}

double f[55][10][10][10];
void dp() {
	for(int i=1; i<=50; i++) 
		for(int a=0; a<=7; a++)
			for(int b=0; b<=7-a; b++)
				for(int c=0; c<=7-a-b; c++) {
					double &now = f[i][a][b][c], t = 1.0 / (a+b+c+1);
					now += t * (f[i-1][a][b][c] + 1);
					if(a) now += a * t * f[i-1][a-1][b][c];
					if(a + b + c < 7) {
						if(b) now += b * t * f[i-1][a+1][b-1][c+1];
						if(c) now += c * t * f[i-1][a][b+1][c];
					} else {
						if(b) now += b * t * f[i-1][a+1][b-1][c];
						if(c) now += c * t * f[i-1][a][b+1][c-1];
					}
				}
}
int k, a, b, c;
int main() {
	freopen("in", "r", stdin);
	dp();
	int T = read();
	while(T--) {
		k=read(); a=read(); b=read(); c=read();
		double ans = f[k][a][b][c];
		//ans = min(ans, 30.00);
		printf("%.2lf
", ans);
	}
}