CodeForces 347B Fixed Points


You are allowed to swap two elements of the permutation at most once.

求a[i]==i的个数，可以交换两个元素一回。

#include<stdio.h>
#include<iostream>
#include<math.h>
#include<string.h>
#include<iomanip>
#include<stdlib.h>
#include<ctype.h>
#include<algorithm>
#include<deque>
#include<functional>
#include<iterator>
#include<vector>
#include<list>
#include<map>
#include<queue>
#include<set>
#include<stack>
#define CPY(A, B) memcpy(A, B, sizeof(A))
typedef long long LL;
typedef unsigned long long uLL;
const int MOD = 1e9 + 7;
const int INF = 0x3f3f3f3f;
const LL INFF = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-9;
const double OO = 1e20;
const double PI = acos (-1.0);
const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, 1, 0, -1};
using namespace std;
const int maxn=1e5+5;
map<int,int>rev;
int main() {
int n,cnt=0,t;
scanf ("%d",&n);
for (int i=0; i<n; i++) {
scanf ("%d",&t);
if (t==i) { cnt++; }
else {rev[i]=t;}
}
map<int,int>::iterator it=rev.begin();
for (; it!=rev.end(); it++) {
if (rev.find ( (*it).second) !=rev.end() &&rev[ (*it).second]== (*it).first) {
cnt++; break;/*!*/
}
}
if (cnt!=n) {++cnt;}
printf ("%d",cnt);
return 0;
}