hdu 1795（欧拉函数+二分搜索）

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#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;const int N=10010;struct node{int no,val;node() {}node(int a, int b): no(a), val(b) {}}v[N];int eu[N],n;void eular(){int i,j;for(i=2;i<N;i++)if(!eu[i])for(j=i;j<N;j+=i){if(!eu[j]) eu[j]=j;eu[j]=eu[j]/i*(i-1);}}int Query(int x){int l,r,mid;l=0, r=n-1;while(r-l>1){mid=(l+r)/2;if(v[mid].val>x)r=mid;elsel=mid;}if(v[l].val<x && v[r].val>=x)return v[r].no;return v[l].no;}int main(){    // freopen("in","r",stdin);    // freopen("out","w",stdout);    int i,j,t,m,tmp;    memset(eu,0,sizeof(eu));    eular();    for(i=1;i<N;i++)    v[i]=node(i,eu[i]);    tmp=v[1].val;    for(i=2,j=0; i<N;i++)    {    if(v[i].val>tmp) v[j++]=v[i];    tmp=max(tmp,v[i].val);    }    n=j;        scanf("%d",&t);    while(t--)    {    scanf("%d",&m);    printf("%d\n",Query(m));    }    return 0;}

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