Check whether array A is a permutation.
Solution
#include <set>int solution(vector<int> &A) { // write your code in C++11 (g++ 4.8.2) set<int> s; int maximum = 1; for (auto i: A) { if (s.find(i) == s.end()) { s.insert(i); } else { return false; } maximum = max(i, maximum); } return (maximum == s.size());}