bulb-switcher_1_AC.cpp

// This is a simple but very elegant problem, to show the power of math thinking.
// I still remember the day when I explained this to my ex-girlfriend on a dinner table.
// Smiles fade, words echo, but science never dies.
// 相聚又分离，总是走在漫长的路上。
#include <cmath>
using std::sqrt;

class Solution {
public:
    int bulbSwitch(int n) {
        return (int)sqrt(n);
    }
};