lc279贪心

从count=1一直遍历到n，找到的第一个符合条件的count就是返回结果。

class Solution {
  Set<Integer> square_nums = new HashSet<Integer>();

  protected boolean is_divided_by(int n, int count) {
    if (count == 1) {
      return square_nums.contains(n);
    }

    for (Integer square : square_nums) {
      if (is_divided_by(n - square, count - 1)) {
        return true;
      }
    }
    return false;
  }

  public int numSquares(int n) {
    this.square_nums.clear();

    for (int i = 1; i * i <= n; ++i) {
      this.square_nums.add(i * i);
    }

    int count = 1;
    for (; count <= n; ++count) {
      if (is_divided_by(n, count))
        return count;
    }
    return count;
  }
}