Solution.cpp

/**
 * Definition for an infinite stream.
 * class InfiniteStream {
 * public:
 *     InfiniteStream(vector<int> bits);
 *     int next();
 * };
 */
class Solution {
public:
    int findPattern(InfiniteStream* stream, vector<int>& pattern) {
        long long a = 0, b = 0;
        int m = pattern.size();
        int half = m >> 1;
        long long mask1 = (1LL << half) - 1;
        long long mask2 = (1LL << (m - half)) - 1;
        for (int i = 0; i < half; ++i) {
            a |= (long long) pattern[i] << (half - 1 - i);
        }
        for (int i = half; i < m; ++i) {
            b |= (long long) pattern[i] << (m - 1 - i);
        }
        long x = 0, y = 0;
        for (int i = 1;; ++i) {
            int v = stream->next();
            y = y << 1 | v;
            v = (int) ((y >> (m - half)) & 1);
            y &= mask2;
            x = x << 1 | v;
            x &= mask1;
            if (i >= m && a == x && b == y) {
                return i - m;
            }
        }
    }
};