441. Arranging Coins

static int wing=[]()
{
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();

class Solution 
{
public:
    int arrangeCoins(int n) 
    {
        return sqrt((long long)n*2+0.25)-0.5;
    }
};

直接数学公式解题