UVa 1620 Lazy Susan (找规律)

题意：给 n 个数，每次可以把4个连续的数字翻转，问你能不能形成1-n的环状排列。

析：找一下奇偶性，写几个数试试，就会找到规律。

代码如下：

#include <cstdio>
#include <string>
#include <cstdlib>
#include <cmath>
#include <iostream>
#include <cstring>
#include <set>
#include <queue>
#include <algorithm>
#include <vector>
#include <map>
#include <cctype>
using namespace std ;
typedef long long LL;
typedef pair<int, int> P;
const int INF = 0x3f3f3f3f;
const double inf = 0x3f3f3f3f3f3f3f;
const double eps = 1e-12;
const int maxn = 1e6 + 5;
const int dr[] = {0, 0, -1, 1};
const int dc[] = {-1, 1, 0, 0};
int n;
int a[505];

int main(){
    int T;  cin >> T;
    while(T--){
        scanf("%d", &n);
        int cnt = 0;
        for(int i = 0; i < n; ++i){
            scanf("%d", &a[i]);
            for(int j = 0; j < i; ++j)
                cnt += (a[i] < a[j]);
        }
        if(cnt & 1 && n & 1)  cout << "impossible
";
        else  cout << "possible
";
    }
    return 0;
}