Codeforces Round #431 (Div. 2) B， C

B：
又挂了，，这次因为自己在除的时候没有+ double 错了几次，被hack

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;
#define sf scanf
#define pf printf
#define mem(a,b) memset(a,b,sizeof(a));
#define rep(i,a,b) for(int i=(a);i<=(b);++i)
#define MP make_pair
#define ULL unsigned long long
#define LL   long long
#define inf 0x3f3f3f3f
#define md ((ll+rr)>>1)
#define ls (i<<1)
#define rs (ls|1)
#define eps 1e-5
#define ree freopen("in.txt","r",stdin);
#define bug pf("----------------");

const int N=1010;

struct Node{
    int id,h;
}a[N];
bool use[N];
int n;
bool deng(double l,double r){
    double x=l-eps;
    double y=l+eps;
    if(r<y&&r>x)return true;
    return false;
}
bool ok(int l,int r){
    double tmp=double(a[r].h-a[l].h)/double(r-l);use[l]=1;use[r]=1;
    for(int i=1;i<=n;++i){
        if(use[i])continue;
        if(i<l){
            if(deng(double(a[l].h-a[i].h)/double(l-i),tmp)){use[i]=1;}
        }
        else if(i>l){
            if(deng(double(a[i].h-a[l].h)/double(i-l),tmp))use[i]=1;
        }
    }
    int cnt=0;
    for(int i=1;i<=n;++i){
        if(!use[i]){cnt++;}
    }
    if(cnt==0)return false;
    else if(cnt==1)return true;
    int id=0;
    for(int i=1;i<=n;++i){
        if(!use[i]&&id==0){ use[i]=1;id=i;
        }
        else if(!use[i]&&id){
            if(!deng(double(a[i].h-a[id].h)/double(i-id),tmp))return false;
        }
    }
    cnt=0;
    if(cnt)return false;
    return true;
}
int main(){
    ios::sync_with_stdio(false);
    cin>>n;
    for(int i =1;i<=n;++i){ cin>>a[i].h; a[i].id=i;}
    for(int i=1;i<=min(n,5);++i){
        for(int j=i+1;j<=n;++j){
            memset(use,0,sizeof(use));
            if(ok(i,j)){puts("YES");return 0;}
        }
    }
    puts("NO");
}

C：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;
#define sf scanf
#define pf printf
#define mem(a,b) memset(a,b,sizeof(a));
#define rep(i,a,b) for(int i=(a);i<=(b);++i)
#define MP make_pair
#define ULL unsigned long long
#define LL   long long
#define inf 0x3f3f3f3f
#define md ((ll+rr)>>1)
#define ls (i<<1)
#define rs (ls|1)
#define eps 1e-5
#define ree freopen("in.txt","r",stdin);
#define bug pf("----------------");
#define N 100010
//2017年09月02日10:25:47


int num[N];

int main(){
    num[2]=1;
    for(int i=3;i<=100000;++i){
        num[i]=(i*(i-1))/2;
    }
    int k;sf("%d",&k);
    if(k==0){puts("a");return 0;}
    for(char c='a';c<='z';++c){
        int cnt=2;
        while(num[cnt+1]<=k){++cnt;}
                k-=num[cnt];
        rep(i,1,cnt){
            pf("%c",c);
        }
        if(k==0)break;
    }puts("");
}