主要是要先弄清楚格雷编码的整个过程 公式为：G(i) = i ^ (i/2);
如 n = 3:
G(0) = 000,
G(1) = 1 ^ 0 = 001 ^ 000 = 001
G(2) = 2 ^ 1 = 010 ^ 001 = 011
G(3) = 3 ^ 1 = 011 ^ 001 = 010
G(4) = 4 ^ 2 = 100 ^ 010 = 110
G(5) = 5 ^ 2 = 101 ^ 010 = 111
G(6) = 6 ^ 3 = 110 ^ 011 = 101
G(7) = 7 ^ 3 = 111 ^ 011 = 100

        //异或 ^相同为0,不同为1List ret = new ArrayList<>();for(int i = 0; i < 1<<n; ++i) ret.add(i ^ i>>1);return ret;

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