2015 Multi-University Training Contest 3 hdu 5323 Solve this interesting problem

Solve this interesting problem

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 1479    Accepted Submission(s): 423

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=n contains 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

 

解题：搜索

 

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
const LL INF = 0x3f3f3f3f3f3f3f3f;
LL X,Y,ret;
void dfs(LL L,LL R) {
    if(R >= ret || L < 0) return;
    if(L == 0) {
        ret = min(ret,R);
        return;
    }
    if(R - L + 1 > L) return;
    dfs(2*L - R - 2,R);
    dfs(2*L - R - 1,R);
    dfs(L,2*R - L);
    dfs(L,2*R - L + 1);
}

int main() {
    while(~scanf("%I64d%I64d",&X,&Y)) {
        ret = INF;
        dfs(X,Y);
        printf("%I64d
",ret == INF?-1:ret);
    }
    return 0;
}