2019杭电多校第十场

1003 Valentine’s Day

从大到小不断组合，如果开心1次的概率大于开心0次概率就可以break了
因为x会越来越小

#include
#define fo(i,a,b) for(i=a;i<=b;i++)
#define fd(i,a,b) for(i=a;i>=b;i--)
using namespace std;
int T,n,i,k;
double a[10005],b[10005],c[10005];
double s,p,x,y,t;
int main()
{
    scanf("%d",&T);
    while (T--)
    {
        scanf("%d",&n);
        fo(i,1,n) scanf("%lf",&a[i]);
        sort(a+1,a+n+1);
        x = a[n]; y = 1 - a[n];
        fd(i,n-1,1)
        {
            if (y < x) break;
            x = x + a[i] * (y - x);
            y = y * (1 - a[i]);
        }
        printf("%.12lf\n",x);
    }
    return 0;
}

1005 Welcome Party

先对x从大到小排序，枚举x，那么比x大的那一部分显然都要扔到另一边，比x小的那一部分挑一个和x最接近的扔到另一边

#include
#define fo(i,a,b) for(i=a;i<=b;i++)
#define fd(i,a,b) for(i=a;i>=b;i--)
#define N 100005
using namespace std;
struct www{long long a,b;} f[N];
int T,n,i;
long long pre,res,s1,s2,A,B;
bool cmp(const www &x,const www &y) {return x.a > y.a;}
int main()
{
    //freopen("1.in","r",stdin);
    //freopen("mine.out","w",stdout);
    scanf("%d",&T);
    while (T--)
    {
        scanf("%d",&n);
        fo(i,1,n) scanf("%lld%lld",&f[i].a,&f[i].b);
        sort(f+1,f+n+1,cmp);
        pre = -1;
        multiset<long long> s;
        fo(i,1,n) s.insert(f[i].b);
        res = 1e18;
        fo(i,1,n)
        {
            s1 = f[i].a;
            s.erase(s.lower_bound(f[i].b));
            auto it=s.lower_bound(f[i].a);
            if (it!=s.end()) A=*it; else A = -1;
            if(it!=s.begin()) B=*(--it); else B = -1;
            if (A == -1 && B == -1) s2 = 0;
            if (B == -1) s2 = A; else
            if (A == -1) s2 = B; else
            if (abs(f[i].a-A) < abs(f[i].a-B)) s2 = A; else s2 = B;
            if (pre > s2 && pre != -1) s2 = pre;
            if (abs(f[i].a-pre) < abs(f[i].a-s2) && pre != -1) s2 = pre;
            res = min(res,abs(s1-s2));
            pre = max(pre,f[i].b);
        }
        cout<<res<<endl;
    }
}

1009 Block Breaker

每次敲掉一个块之后往四个方向搜索即可

#include
#define fo(i,a,b) for(i=a;i<=b;i++)
#define fd(i,a,b) for(i=a;i>=b;i--)
#define N 2005
using namespace std;
int a[N][N];
int res,T,n,m,q,i,j,x,y;
void dfs(int x,int y)
{
    int numx,numy;
    if (a[x][y] == -1) return;
    if (a[x][y] == 0) return;
    numx = numy = 0;
    if (a[x-1][y] == 0 || a[x+1][y] == 0) numx++;
    if (a[x][y+1] == 0 || a[x][y-1] == 0) numy++;
    if (numx && numy)
    {
        a[x][y] = 0;
        res++;
        dfs(x+1,y); dfs(x-1,y);
        dfs(x,y+1); dfs(x,y-1);
    }
}
int main()
{
    scanf("%d",&T);
    while (T--)
    {
        scanf("%d%d%d",&n,&m,&q);
        fo(i,1,n) fo(j,1,m) a[i][j] = 1;
        fo(i,0,n+1) a[i][0] = a[i][m+1] = -1;
        fo(j,0,m+1) a[0][j] = a[n+1][j] = -1;
        while (q--)
        {
            res = 0;
            scanf("%d%d",&x,&y);
            if (a[x][y] == 0) {printf("%d\n",res); continue;}
            a[x][y] = 0; res++;
            dfs(x+1,y); dfs(x-1,y);
            dfs(x,y+1); dfs(x,y-1);
            printf("%d\n",res);
        }
    }
}