Submission #96433

#	Time	Username	Problem	Language	Result	Execution time	Memory
96433		easrui	Mobile (BOI12_mobile)	C++14	100 / 100	356 ms	63744 KiB

mobile

#include <bits/stdc++.h>
using namespace std;
const int MN = 1e6+5;
int N,L,C[MN],num[MN],cur,pos;
long long X[MN],Y[MN],A[MN],B[MN];
long double Ipos[MN],x,ans,tmp;

bool cmp(int a, int b)
{
    if(A[a]==A[b]) return B[a]<B[b];
    return A[a]>A[b];
}

long double getI(int a, int b)
{
    if(A[a]==A[b]) return L;
    return (long double)(B[a]-B[b])/(A[b]-A[a]);
}

int main()
{
    ios_base::sync_with_stdio(0),cin.tie(0);
    //freopen("C:\\Users\\user\\Downloads\\mobile_tests\\mobile.i03d","r",stdin);
    cin >> N >> L;
    for(int i=0; i<N; i++){
        cin >> X[i] >> Y[i];
        A[i] = X[i]*(-2);
        B[i] = X[i]*X[i]+Y[i]*Y[i];
        num[i] = i;
    }
    sort(num,num+N,cmp);
    Ipos[pos] = 0;
    C[pos] = num[0];
    for(int i=1; i<N; i++){
        cur = num[i];
        while(1){
            if(pos==-1){
                Ipos[++pos] = 0;
                C[pos] = cur;
                break;
            }
            x = getI(C[pos],cur);
            if(x>=L) break;
            if(x>Ipos[pos]){
                Ipos[++pos] = x;
                C[pos] = cur;
                break;
            }
            pos--;
        }
    }
    Ipos[pos+1] = L;
    for(int i=0; i<=pos; i++){
        cur = C[i];
        tmp = max((Ipos[i]-X[cur])*(Ipos[i]-X[cur]),(Ipos[i+1]-X[cur])*(Ipos[i+1]-X[cur]))+Y[cur]*Y[cur];
        ans = max(ans,tmp);
    }
    cout << fixed;
    cout.precision(4);
    cout << sqrt(ans);
}

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