hdu 5328 简单题

等差和等比各扫一遍即可。

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdio>
#include <cmath>
using namespace std;

const int N = 1000000;
const double eps = 1e-8;
int a[N];

int main ()
{
    int t;
    scanf("%d", &t);
    while ( t-- )
    {
        int n;
        scanf("%d", &n);
        for ( int i = 0; i < n; i++ ) scanf("%d", a + i);
        if ( n == 1 || n == 2 )
        {
            printf("%d
", n);
            continue;
        }
        int ans = 2, i = 0;
        while ( i < n - 2 )
        {
            int d = a[i] - a[i + 1];
            int j = i + 1;
            while ( j < n - 1 && a[j] - a[j + 1] == d )
            {
                j++;
            }
            ans = max( ans, j - i + 1 );
            i = j;
        }
        i = 0;
        while ( i < n - 2 )
        {
            double d = a[i] * 1.0 / a[i + 1];
            int j = i + 1;
            while ( j < n - 1 && fabs( a[j] * 1.0 / a[j + 1] - d ) < eps )
            {
                j++;
            }
            ans = max( ans, j - i + 1 );
            i = j;
        }
        printf("%d
", ans);
    }
    return 0;
}