PAT-1144（The Missing Number）set的使用，简单题

The Missing Number

PAT-1144

#include<iostream>
#include<cstring>
#include<string>
#include<algorithm>
#include<cstdio>
#include<sstream>
#include<set>
using namespace std;
const int maxn=100005; 
set<int>se;
int main(){
	int  n;
	cin>>n;
	for(int i=0;i<n;i++){
		int a;
		cin>>a;
		if(a>0)
			se.insert(a);
	}
	if(se.empty()){
		cout<<1<<endl;
		return 0;
	}
	set<int>::iterator it=se.begin();
	int pre=*it;
	it++;
	for(;it!=se.end();it++){
		int now=*it;
//		cout<<now<<endl;
		if(now!=pre+1){
			cout<<pre+1<<endl;
			return 0;
		}else pre=now;
	}
	cout<<pre+1<<endl;
	return 0;
}