hdu 3833

暴力，有技巧，确定a[i2]的值，先从0~i2找a[i1]的值来计算a[i3]的值，当i2>n/2时，从i2~n-1找a[i3]的值来计算a[i1]的值

#include<stdio.h>int hash[10010],a[10010];int main(){int i,j,n,t,k,flag;scanf("%d",&t);while(t--){flag=0;scanf("%d",&n);for(i=0;i<n;i++){scanf("%d",&a[i]);hash[a[i]]=i;}for(i=1;i<n/2;i++){for(j=0;j<i;j++){k=2*a[i]-a[j];if(k<=0||k>n)continue;if(hash[k]>i){flag=1;break;}}if(flag==1)break;}for(i;i<n-1;i++){for(j=i+1;j<n;j++){ k=2*a[i]-a[j]; if(k<=0||k>n)continue;if(hash[k]<i){flag=1;break;}}if(flag==1)break;}if(flag==1)puts("Y");else puts("N");}return 0;}