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GrayCode.java

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import java.util.ArrayList;

/**

* The gray code is a binary numeral system where two successive values differ

* in only one bit.

*

* Given a non-negative integer n representing the total number of bits in the

* code, print the sequence of gray code. A gray code sequence must begin with 0.

*

* For example, given n = 2, return [0,1,3,2]. Its gray code sequence is:

*

* 00 - 0

* 01 - 1

* 11 - 3

* 10 - 2

*

* Note:

*

* For a given n, a gray code sequence is not uniquely defined.

*

* For example, [0,2,3,1] is also a valid gray code sequence according to the above definition.

*

* For now, the judge is able to judge based on one instance of gray code sequence. Sorry about that.

*/

public class GrayCode {

public ArrayList<Integer> grayCode(int n) {

ArrayList<Integer> result = new ArrayList<Integer>();

if (n == 0) {

result.add(0);

return result;

}

;

result.add(0);

result.add(1);

for (int i = 1; i < n; i++) {

ArrayList<Integer> tmp = new ArrayList<Integer>(result);

Integer a = 1 << i;

for (int k = result.size() - 1; k >= 0; k--) {

tmp.add(result.get(k) + a);

}

result = tmp;

}

return result;

}

}