leetcode练习：441. Arranging Coins

You have a total of n coins that you want to form in a staircase shape, where every k-th row must have exactly k coins.

Given n, find the total number of full staircase rows that can be formed.

n is a non-negative integer and fits within the range of a 32-bit signed integer.

Example 1:

n = 5

The coins can form the following rows:
¤
¤ ¤
¤ ¤

Because the 3rd row is incomplete, we return 2.

Example 2:

n = 8

The coins can form the following rows:
¤
¤ ¤
¤ ¤ ¤
¤ ¤

Because the 4th row is incomplete, we return 3.

然后后来，我才想起来还有Math.sqrt就可以不用这样做了，直接返回一个表达式即可，噗。

var arrangeCoins = function(n) {
    var cur=0,i=1;
    
    if(n==0)
        return 0;
    
    while(1){
        cur = i + (i*i - i)/2;
        if(cur>n){
            return i-1;
        } else if(cur==n){
            return i;
        }
        i++;
    }
};