Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.
Example
Given n = 12, return 3 because 12 = 4 + 4 + 4
Given n = 13, return 2 because 13 = 4 + 9
[LintCode] Perfect Squares 完全平方数
原文：http://www.cnblogs.com/grandyang/p/5448521.html