Codeforces Round #287 (Div. 2) C. Guess Your Way Out! 数学

C. Guess Your Way Out!
time limit per test1 second
memory limit per test256 megabytes
inputstandard input
outputstandard output
Amr bought a new video game “Guess Your Way Out!”. The goal of the game is to find an exit from the maze that looks like a perfect binary tree of height h. The player is initially standing at the root of the tree and the exit from the tree is located at some leaf node.

Let’s index all the leaf nodes from the left to the right from 1 to 2h. The exit is located at some node n where 1 ≤ n ≤ 2h, the player doesn’t know where the exit is so he has to guess his way out!

Amr follows simple algorithm to choose the path. Let’s consider infinite command string “LRLRLRLRL…” (consisting of alternating characters ‘L’ and ‘R’). Amr sequentially executes the characters of the string using following rules:

Character ‘L’ means “go to the left child of the current node”;
Character ‘R’ means “go to the right child of the current node”;
If the destination node is already visited, Amr skips current command, otherwise he moves to the destination node;
If Amr skipped two consecutive commands, he goes back to the parent of the current node before executing next command;
If he reached a leaf node that is not the exit, he returns to the parent of the current node;
If he reaches an exit, the game is finished.
Now Amr wonders, if he follows this algorithm, how many nodes he is going to visit before reaching the exit?

Input
Input consists of two integers h, n (1 ≤ h ≤ 50, 1 ≤ n ≤ 2h).

Output
Output a single integer representing the number of nodes (excluding the exit node) Amr is going to visit before reaching the exit by following this algorithm.

Sample test(s)
input
1 2
output
2
input
2 3
output
5
input
3 6
output
10
input
10 1024
output
2046
Note
A perfect binary tree of height h is a binary tree consisting of h + 1 levels. Level 0 consists of a single node called root, level h consists of 2h nodes called leaves. Each node that is not a leaf has exactly two children, left and right one.

Following picture illustrates the sample test number 3. Nodes are labeled according to the order of visit.
题意是，有一个完全二叉树，树的叶子结点从1排到2^h,给一段序列lrlrlr….这样交替，l表示向左走，r表示向右走，如果到叶子结点，返回父结点如果，已经访问过，就不动，若有两次不动，则返回父结点，最后，给出目标结点，问需要多少次可以到达目标结点。
画个图就可以发现，如果前一个是l这步是r,则要加1,如果前一个是r这步是l,则要加2^h,所以只需要求出每一位，与前一位比较奇偶性，如果同奇偶加2^h,否则加1

#define INF 9000000000
#define EPS (double)1e-9
#define mod 1000000007
#define PI 3.14159265358979
//*******************************************************************************/
#endif
#define N 55
#define M 100005
#define maxn 205
#define MOD 1000000000000000007
ll h,n,ten[N],ans[N],ansi,sum;
int main()
{
    ten[0] = 1;
    for(int i = 1;i<N;i++)
    ten[i] = ten[i-1] * 2;
    while(cin>>h)
    {
        cin>>n;
        ansi = 0;
        ll nn = ten[h] + n - 1;
        while(nn){
            ans[ansi++] = nn;
            nn/=2;
        }
        nn = n;sum = 0;
        bool flag = true;
        //cout<<ans[ansi-1]<<" ";
        for(int i=ansi-2;i>=0;i--){
            //cout<<ans[i]<<" ";
            sum+= (ans[i+1] & 1) == (ans[i] & 1)? ten[h]:1;
            h--;
        }
        cout<<sum<<endl;
    }
    return 0;
}