xjoi奋斗群群赛11

群赛地址:

https://vjudge.net/contest/186188#problem

(缺后2题)

A - The Wall

 CodeForces - 340A 

题意:给出一段整数区间和两个数a,b,求区间中是a,b的倍数的数的个数.

题解:

#include<bits/stdc++.h>using namespace std;int gcd(const int &a,const int &b){return b?gcd(b,a%b):a;}int lcm(const int &a,const int &b){return a*b/gcd(a,b);}int main(){int x,y,a,b,g,l,r,ret=0;cin>>x>>y>>a>>b;g=lcm(x,y);ret=b/g-a/g;if(a%g==0)ret++;cout<<ret;}

B - Maximal Area Quadrilateral

 CodeForces - 340B 

题意:平面上有一些点,求以其中的点为顶点的四边形的最大值.

思路:暴力枚举四边形中最左和最右两点,其中最大面积的四边形就是与最上点,最下点构成的四边形.

题解;

#include <bits/stdc++.h>using namespace std;struct pt{    int x,y;}s[303];int n;int cross3(int a,int b,int c){    return s[a].x*s[b].y+s[b].x*s[c].y+s[c].x*s[a].y          -(s[a].y*s[b].x+s[b].y*s[c].x+s[c].y*s[a].x);}int main(){    scanf("%d",&n);    for(int i=1;i<=n;i++) scanf("%d %d",&s[i].x,&s[i].y);    int ans=0;    for(int i=1;i<=n;i++){        for(int j=i+1;j<=n;j++){            int ans1=0,ans2=0;            for(int k=1;k<=n;k++){                if(cross3(i,j,k)>0) ans2=max(ans2,cross3(i,j,k));                else ans1=max(ans1,-cross3(i,j,k));            }            if(ans1==0||ans2==0) continue;            ans=max(ans,ans1+ans2);        }    }    printf("%lf\n",ans/2.0);    return 0;}

C - Tourist Problem

 CodeForces - 340C 

题意:一条路上有一些目标,一个人从0开始,每次跳到一个点.求他所有跳的可能性中总路程的平均数.

错的代码:

#include<bits/stdc++.h>using namespace std;long long gcd(long long a,long long b){return b?gcd(b,a%b):a;}long long n,a[100010],ans;int main(){cin>>n;for(int i=1;i<=n;i++)cin>>a[i];for(int i=1;i<n;i++){ans+=2*i*(n-i)*(a[i+1]-a[i])+a[i];}ans+=a[n];long long d=gcd(ans,n);cout<<ans/d<<" "<<n/d;}

题解:

#include <bits/stdc++.h>using namespace std;#define ll long longll a[100010];int main(){ll n; scanf("%lld", &n);for (ll i = 0; i < n; i++) scanf("%lld", &a[i]);sort(a, a + n);ll s1 = 0, s2 = 0;for (ll i = 0; i < n; i++){s2 += i * a[i] - s1;s1 += a[i];}ll num = 2*s2 + s1, d = n;for (ll i = 2; i <= d; i++){while (num % i == 0 && d % i == 0){ num /= i; d /= i; }}printf("%lld %lld", num, d);return 0;}

D - Bubble Sort Graph

 CodeForces - 340D 

E - Iahub and Permutations

 CodeForces - 340E