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每次交換：逆序對的數量+1或者-1；

假設最后逆序對數量為 sum;

①x+y=3n;

②x-y=sum;

-> 3n+sum為偶數；

所以 n 和 sum 必須奇偶一樣；

#include<iostream> #include<cstdio> #include<algorithm> #include<cstdlib> #include<cstring> #include<string> #include<cmath> #include<map> #include<set> #include<vector> #include<queue> #include<bitset> #include<ctime> #include<deque> #include<stack> #include<functional> #include<sstream> //#include<cctype> //#pragma GCC optimize(2) using namespace std; #define maxn 1000005 #define inf 0x7fffffff //#define INF 1e18 #define rdint(x) scanf("%d",&x) #define rdllt(x) scanf("%lld",&x) #define rdult(x) scanf("%lu",&x) #define rdlf(x) scanf("%lf",&x) #define rdstr(x) scanf("%s",x) typedef long long ll; typedef unsigned long long ull; typedef unsigned int U; #define ms(x) memset((x),0,sizeof(x)) const long long int mod = 1e9 + 7; #define Mod 1000000000 #define sq(x) (x)*(x) #define eps 1e-4 typedef pair<int, int> pii; #define pi acos(-1.0) //const int N = 1005; #define REP(i,n) for(int i=0;i<(n);i++) typedef pair<int, int> pii; inline ll rd() {ll x = 0;char c = getchar();bool f = false;while (!isdigit(c)) {if (c == '-') f = true;c = getchar();}while (isdigit(c)) {x = (x << 1) + (x << 3) + (c ^ 48);c = getchar();}return f ? -x : x; }ll gcd(ll a, ll b) {return b == 0 ? a : gcd(b, a%b); } int sqr(int x) { return x * x; }/*ll ans; ll exgcd(ll a, ll b, ll &x, ll &y) {if (!b) {x = 1; y = 0; return a;}ans = exgcd(b, a%b, x, y);ll t = x; x = y; y = t - a / b * y;return ans; } */int n; int a[maxn]; int b[maxn]; int c[maxn];void add(int x) {while (x <= n) {c[x]++; x += x & -x;} } int query(int x) {int res = 0;while (x > 0) {res += c[x]; x -= x & -x;}return res; } int main() {//ios::sync_with_stdio(0);rdint(n);for (int i = 1; i <= n; i++) {rdint(a[i]); b[i] = a[i];}sort(b + 1, b + 1 + n);int ans = 0;for (int i = 1; i <= n; i++) {add(lower_bound(b + 1, b + 1 + n, a[i]) - b);ans += (i - query(lower_bound(b + 1, b + 1 + n, a[i] + 1) - b - 1));}if ((ans & 1) == (n & 1)) {cout << "Petr" << endl;}else cout << "Um_nik" << endl;return 0; }

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轉載于:https://www.cnblogs.com/zxyqzy/p/10273657.html

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