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H - H

Time Limit:4000MS     Memory Limit:65536KB     64bit IO Format:%I64d & %I64u

Submit   Status

Description

Given a permutation P of 1 to N, YY wants to know whether there exists such three elements P[i   ₁], P[i   ₂], P[i   ₃] that  
P[i   ₁]-P[i   ₂]=P[i   ₂]-P[i   ₃], 1<=i   ₁<i   ₂<i   ₃<=N.

 

Input

The first line is T(T<=60), representing the total test cases.  
Each test case comes two lines, the former one is N, 3<=N<=10000, the latter is a permutation of 1 to N.

 

Output

For each test case, just output 'Y' if such i   ₁, i   ₂, i   ₃  can be found, else 'N'.

 

Sample Input

       

         2
3
1 3 2
4
3 2 4 1 
       

 

Sample Output

       

         N
Y 
       

 

#include <stdio.h>
#include <string.h>
int hs[100000];
int ch[100000];         //再次强调数组大小问题，要开足
int main()
{
    int T,n,i,j,flag;
    scanf("%d",&T);
    while(T--)
    {
        memset(hs,0,sizeof(hs));
        flag=0;
        scanf("%d",&n);
        for(i=0; i<n; i++)
        {
            scanf("%d",&ch[i]);
            hs[ch[i]]=i;
        }
        for(i=0; i<n-2; i++)
            for(j=i+2; j<n; j++)
            {
                int a=ch[i]+ch[j];
                if(a%2!=0)                     //注意偶数的判断，如果是奇数就直接略过
                    continue;
                else
                {
                    if(hs[a/2]>i&&hs[a/2]<j)
                    {
                        flag=1;
                        break;
                    }
                }
            }
        if(flag)
            printf("Y\n");
        else
            printf("N\n");
    }
}