hdu 5323 Solve this interesting problem dfs搜索

Solve this interesting problem

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 1431    Accepted Submission(s): 404

Problem Description

Have you learned something about segment tree? If not, don’t worry, I will explain it for you.
Segment Tree is a kind of binary tree, it can be defined as this:
- For each node u in Segment Tree, u has two values:  Lu and  Ru.
- If  Lu=Ru, u is a leaf node. 
- If  Lu≠Ru, u has two children x and y,with  Lx=Lu, Rx=⌊Lu+Ru2⌋, Ly=⌊Lu+Ru2⌋+1, Ry=Ru.
Here is an example of segment tree to do range query of sum.



Given two integers L and R, Your task is to find the minimum non-negative n satisfy that: A Segment Tree with root node's value  Lroot=0 and  Rroot=ncontains a node u with  Lu=L and  Ru=R.

 

Input

The input consists of several test cases. 
Each test case contains two integers L and R, as described above.
0≤L≤R≤109
LR−L+1≤2015

 

Output

For each test, output one line contains one integer. If there is no such n, just output -1.

 

Sample Input

6 7 10 13 10 11

 

Sample Output

7 -1 12

 

Source

2015 Multi-University Training Contest 3

给出线段树的一个区间，问满足的树【0，n】的n

由于，线段树的每个节点，的左区间可能比右区间大一，所以向上回溯的时候，就出现了四种情况，记录len为区间长度

还需要剪枝，如果r>=res 则不需要继续了，或者r>2*rr也不需要了

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