Add olinfo task police: 100/100

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Author: Stypox

olinfo/police/README.md

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+# [Police Investigation (police)](https://training.olinfo.it/#/task/ois_police/statement)
+Score: 100/100

olinfo/police/main.cpp

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+#pragma GCC optimize ("O3")
+#include <bits/stdc++.h>
+using namespace std;
+
+#define int int64_t
+#define float long double
+
+ifstream in{"input.txt"};
+ofstream out{"output.txt"};
+#ifdef DEBUG
+template<class A,class B>ostream&operator<<(ostream&o,const pair<A,B>&p){cout<<"("<<p.first<<", "<<p.second<<")";return o;}
+template<class T,typename=typename enable_if<!is_same<T, string>::value,decltype(*begin(declval<T>()))>::type>ostream&operator<<(ostream&o,const T&v){cout<<"[";for(auto it=v.begin();it!=v.end();++it){if(it!=v.begin()){cout<<", ";}cout<<*it;}cout<<"]";return o;}
+void deb(){cout<<"\n";}template<class T,class...Ts>void deb(const T&t,const Ts&...args){cout<<t;if(sizeof...(args)!=0){cout<<" ";}deb(args...);}
+#else
+#define deb(...)
+#endif
+
+signed main() {
+int N,K;
+ in>>N>>K;
+ K--;
+
+ vector<int> V(N);
+ for(int n=0;n<N;++n){
+ in>>V[n];
+ V[n]--;
+ }
+
+ int cnt=0;
+ vector<bool> vis(N, false);
+
+ int cur=0;
+ while(cur != K && vis[cur] == false) {
+ vis[cur] = true;
+ cur = V[cur];
+ ++cnt;
+ }
+
+ if (cur != K) {
+ cnt=-1;
+ }
+ out<<cnt<<endl;
+}