Codeforces div.2 B. The Child and Set
题目例如以下:
At the children's day, the child came to Picks's house, and messed his house up. Picks was angry at him. A lot of important things were lost, in particular the favorite set of Picks.
Fortunately, Picks remembers something about his set S:
- its elements were distinct integers from 1 to limit;
- the value of was equal to sum; here lowbit(x) equals 2k where k is the position of the first one in the binary representation of x. For example, lowbit(100102) = 102, lowbit(100012) = 12, lowbit(100002) = 100002 (binary representation).
Can you help Picks and find any set S, that satisfies all the above conditions?
The first line contains two integers: sum, limit (1 ≤ sum, limit ≤ 105).
In the first line print an integer n (1 ≤ n ≤ 105), denoting the size of S. Then print the elements of set S in any order. If there are multiple answers, print any of them.
If it's impossible to find a suitable set, print -1.
5 5
2 4 5
4 3
3 2 3 1
5 1
-1
这道题求出二进制的低位(从最先出现1的位置截断),事实上就是位运算。恰好我不熟悉位运算。罪过啊。。
。于是恶补了位运算,求二进制低位用i&-i,求最后以为i&1,左移i<<1,右移i>>1,然后从limit枚举。假设小于sum,就增加答案中.
自己的代码太丑了。粘贴一下别人的美丽的代码: