153 lines
3.4 KiB
C++
153 lines
3.4 KiB
C++
// Source : https://oj.leetcode.com/problems/gray-code/
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// Author : Hao Chen
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// Date : 2014-06-20
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/**********************************************************************************
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*
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* The gray code is a binary numeral system where two successive values differ in only one bit.
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*
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* Given a non-negative integer n representing the total number of bits in the code,
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* print the sequence of gray code. A gray code sequence must begin with 0.
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*
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* For example, given n = 2, return [0,1,3,2]. Its gray code sequence is:
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*
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* 00 - 0
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* 01 - 1
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* 11 - 3
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* 10 - 2
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*
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* Note:
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* For a given n, a gray code sequence is not uniquely defined.
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*
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* For example, [0,2,3,1] is also a valid gray code sequence according to the above definition.
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*
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* For now, the judge is able to judge based on one instance of gray code sequence. Sorry about that.
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*
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**********************************************************************************/
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#include <stdio.h>
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#include <stdlib.h>
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#include <time.h>
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#include <iostream>
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#include <vector>
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using namespace std;
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/*
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* I designed the following stupid algorithm base on the blow observation
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*
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* I noticed I can use a `mirror-like` binary tree to figure out the gray code.
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*
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* For example:
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*
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* 0
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* __/ \__
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* 0 1
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* / \ / \
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* 0 1 1 0
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* So, the gray code as below: (top-down, from left to right)
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*
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* 0 0 0
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* 0 0 1
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* 0 1 1
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* 0 1 0
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*
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* 0
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* _____/ \_____
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* 0 1
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* __/ \__ __/ \__
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* 0 1 1 0
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* / \ / \ / \ / \
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* 0 1 1 0 0 1 1 0
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*
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* So, the gray code as below:
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*
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* 0 0 0 0
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* 0 0 0 1
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* 0 0 1 1
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* 0 0 1 0
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* 0 1 1 0
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* 0 1 1 1
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* 0 1 0 1
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* 0 1 0 0
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*/
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vector<int> grayCode01(int n) {
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vector<int> v;
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//n = 1<<n;
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int x =0;
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v.push_back(x);
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for(int i=0; i<n; i++){
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int len = v.size();
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for (int j=0; j<len; j++){
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x = v[j]<<1;
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if (j%2==0){
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v.push_back(x);
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v.push_back(x+1);
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}else{
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v.push_back(x+1);
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v.push_back(x);
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}
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}
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v.erase(v.begin(), v.begin()+len);
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}
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return v;
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}
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/*
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* Actually, there is a better way.
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* The mathematical way is: (num >> 1) ^ num;
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* Please refer to http://en.wikipedia.org/wiki/Gray_code
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*/
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vector<int> grayCode02(int n) {
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vector<int> ret;
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int size = 1 << n;
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for(int i = 0; i < size; ++i) {
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ret.push_back((i >> 1)^i);
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}
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return ret;
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}
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//random invoker
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vector<int> grayCode(int n) {
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srand(time(0));
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if (rand()%2){
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return grayCode01(n);
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}
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return grayCode02(n);
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}
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void printBits(int n, int len){
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for(int i=len-1; i>=0; i--) {
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if (n & (1<<i)) {
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printf("1");
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}else{
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printf("0");
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}
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}
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}
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void printVector(vector<int>& v, int bit_len)
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{
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vector<int>::iterator it;
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for(it=v.begin(); it!=v.end(); ++it){
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//bitset<bit_len> bin(*it);
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printBits(*it, bit_len);
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cout << " ";
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//cout << *it << " ";
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}
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cout << endl;
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}
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int main(int argc, char** argv)
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{
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int n = 2;
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if (argc>1){
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n = atoi(argv[1]);
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}
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vector<int> v = grayCode(n);
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printVector(v, n);
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return 0;
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}
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