Codeforces Round #276 (Div. 1) B. Maximum Value

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数学题

但是我用的是暴力去求解的

先去重，再根据数量分类讨论（注意，去重的时候可以选择用计数排序，或者sort+unique函数）

#include <algorithm>#include <iostream>#include <iomanip>#include <cstring>#include <climits>#include <complex>#include <fstream>#include <cassert>#include <cstdio>#include <bitset>#include <vector>#include <deque>#include <queue>#include <stack>#include <ctime>#include <set>#include <map>#include <cmath>#define CLR(x,y) memset(x,y,sizeof(x))#define mp(x,y) make_pair(x,y)#define eps 1e-9#define INF 0x3f3f3f3f#define LLINF 1LL<<62using namespace std;typedef long long ll;typedef long double ld;typedef pair<ll, ll> pll;typedef complex<ld> point;typedef pair<int, int> pii;typedef pair<pii, int> piii;template<class T>inline bool read(T &n){    T x = 0, tmp = 1; char c = getchar();    while((c < '0' || c > '9') && c != '-' && c != EOF) c = getchar();    if(c == EOF) return false;    if(c == '-') c = getchar(), tmp = -1;    while(c >= '0' && c <= '9') x *= 10, x += (c - '0'),c = getchar();    n = x*tmp;    return true;}template <class T>inline void write(T n){    if(n < 0)    {        putchar('-');        n = -n;    }    int len = 0,data[20];    while(n)    {        data[len++] = n%10;        n /= 10;    }    if(!len) data[len++] = 0;    while(len--) putchar(data[len]+48);}//-----------------------------------const int MAXN=1000005;int vis[MAXN];int a[MAXN];int n,cnt;int main(){    read(n);    for(int i=1,t;i<=n;i++)    {        read(t);        vis[t]=1;    }    for(int i=1;i<MAXN;i++)    {        if(!vis[i])continue;        a[++cnt]=i;    }    int ans=0;    if(cnt<=5000)    {        for(int i=1;i<=cnt;i++)            for(int j=i+1;j<=cnt;j++)                ans=max(ans,a[j]%a[i]);                //cout<<a[j]%a[i]<<endl;    }    else    {        for(int i=cnt-1;i;i--)        {            if(ans>=a[i]-1)break;            for(int j=a[i]*2;j-a[i]<=a[cnt];j+=a[i])            {                int u=lower_bound(a+1,a+cnt+1,j)-a;                //cout<<i<<' '<<j<<' '<<u<<' '<<a[u-1]%a[i]<<endl;                ans=max(ans,a[u-1]%a[i]);            }        }    }    printf("%d\n",ans);    return 0;}

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