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.
要处理mid 的越界问题
public int arrangeCoins(int n) {
if (n == 0) return 0;
int beg = 1, end = n;
while (beg + 1 < end) {
long mid = beg + (end - beg) / 2;
if (mid * (mid + 1) / 2 <= n) {
beg = (int)mid;
} else {
end = (int)mid;
}
}
return beg;
}
原文：http://www.cnblogs.com/apanda009/p/7324798.html