#include <iostream>
#include <map>
#include <algorithm>

using namespace std;

map <int, int> m;

int main() {
	m[1] = 100;
	m[2] = 200;
	m[3] = 300;
	for (map <int, int>:: iterator iter = m.begin(); iter != m.end(); ++iter) {
       cout << iter->first << ' ' << iter->second << endl;  
	}
	return 0;
}

这个代码是 $O(n)$ 还是 $O(n log n)$?

有没有更优的方法？