Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
	)

var scanner = bufio.NewScanner(os.Stdin)

const INF = 0x7FFFFFFF

var (
	direction1 = [][]int{ // 奇数段目の移動方向
		{-1, 0}, {1, 0}, {0, -1}, {0, 1}, {1, -1}, {1, 1},
	}
	direction2 = [][]int{ // 偶数段目の移動方向
		{-1, -1}, {0, -1}, {1, 0}, {0, 1}, {-1, 1}, {-1, 0},
	}
)

func main() {
	for scanner.Scan() {
		buf := strings.Split(scanner.Text(), " ")
		m, _ := strconv.Atoi(buf[0])
		n, _ := strconv.Atoi(buf[1])
		if m == 0 && n == 0 {
			break
		}
		// initialize district_map
		/*
			district_map = [
				[-1, -1,  -1,  -1,  -1]
				[-1, INF, INF, INF, -1]
				[-1, INF, INF, INF, -1]
				[-1, INF, INF, INF, -1]
				[-1, INF, INF, INF, -1]
				[-1, -1,  -1,  -1,  -1]
			]
		*/
		district_map := make([][]int, n+2)
		for i := range district_map {
			district_map[i] = make([]int, m+2)
		}
		tmp1 := make([]int, m+2)
		for i := range tmp1 {
			tmp1[i] = -1
		}
		district_map[0] = tmp1
		district_map[n+1] = tmp1
		for i := 1; i < n+1; i++ {
			district_map[i] = make([]int, m+2)
			district_map[i][0] = -1
			district_map[i][m+1] = -1
			for j := 1; j < m+1; j++ {
				district_map[i][j] = INF
			}
		}

		scanner.Scan()
		s, _ := strconv.Atoi(scanner.Text())
		for i := 0; i < s; i++ {
			scanner.Scan()
			buf_ := strings.Split(scanner.Text(), " ")
			x, _ := strconv.Atoi(buf_[0])
			y, _ := strconv.Atoi(buf_[1])
			Search(Point{x, y}, district_map, m, n)
		}
		ans := 0
		scanner.Scan()
		t, _ := strconv.Atoi(scanner.Text())
		for i := 0; i < t; i++ {
			scanner.Scan()
			buf__ := strings.Split(scanner.Text(), " ")
			x, _ := strconv.Atoi(buf__[0])
			y, _ := strconv.Atoi(buf__[1])
			z := Count(Point{x, y}, district_map, m, n)
			ans = max(ans, z)
		}
		fmt.Println(ans)
	}
}

func max(a, b int) int {
	if a < b {
		return b
	}
	return a
}

type Point struct {
	x, y int
}

type Entry struct {
	hop   int
	point Point
}

func Search(p Point, mp [][]int, m, n int) {
	que := make([]Entry, 0)
	que = append(que, Entry{0, p})
	check := make([][]bool, n+2)
	for i := range check {
		check[i] = make([]bool, m+2)
	}
	check[p.y][p.x] = true
	mp[p.y][p.x] = 0
	var direction [][]int
	for len(que) > 0 {
		tmp := que[0]
		que = que[1:]
		dist, point := tmp.hop, tmp.point
		if point.y%2 == 0 {
			direction = direction1
		} else {
			direction = direction2
		}
		for _, d := range direction {
			nx, ny := point.x+d[0], point.y+d[1]
			if !check[ny][nx] && mp[ny][nx] != -1 {
				check[ny][nx] = true
				if mp[ny][nx] > dist+1 {
					mp[ny][nx] = dist + 1
				}
				que = append(que, Entry{dist + 1, Point{nx, ny}})
			}
		}
	}
}

func Count(p Point, mp [][]int, m, n int) int {
	que := make([]Entry, 0)
	que = append(que, Entry{0, p})
	check := make([][]bool, n+2)
	for i := range check {
		check[i] = make([]bool, m+2)
	}
	check[p.y][p.x] = true
	ans := 1
	var direction [][]int
	for len(que) > 0 {
		tmp := que[0]
		que = que[1:]
		dist, point := tmp.hop, tmp.point
		if point.y%2 == 0 {
			direction = direction1
		} else {
			direction = direction2
		}
		for _, d := range direction {
			nx, ny := point.x+d[0], point.y+d[1]
			if !check[ny][nx] && mp[ny][nx] != -1 {
				check[ny][nx] = true
				if mp[ny][nx] > dist+1 {
					ans++
				}
				que = append(que, Entry{dist + 1, Point{nx, ny}})
			}
		}
	}
	return ans
}

C++: #include<iostream>
#include<algorithm>
#include<cmath>
#include<cstdio>
#include<cassert>
#include<vector>
#include<deque>
using namespace std;
typedef pair<int,int> P;
int n,m,cnt;
int mincost[110][110];
bool visited[110][110];
int dx[2][6] = {{-1,+0,1,0,-1,-1},{+0,+1,1,1,0,-1}};
int dy[2][6] = {{-1,-1,0,1,+1,+0},{-1,-1,0,1,1,+0}};
bool f;

void dfs(int x,int y)
{

  deque<P> deq;
  deq.push_back(P(x,y));
  mincost[y][x] = 0;
  cnt = 1;
  while(!deq.empty())
    {
      P p = deq.front(); deq.pop_front();

      for(int i=0;i<6;i++)
	{
	  int nx = p.first + dx[p.second%2][i];
	  int ny = p.second + dy[p.second%2][i];

	  if(!(0 <= nx && nx < m && 0 <= ny && ny < n))
	    continue;

	  if(mincost[ny][nx] > mincost[p.second][p.first] + 1)
	    {
	      if(!visited[ny][nx])
		cnt++;
	      visited[ny][nx] = true;
	      mincost[ny][nx] = mincost[p.second][p.first] + 1;
	      deq.push_back(P(nx,ny));
	    }
	}
    }
}

int main()
{
  while(true)
    {
      cin >> n;
      if(!n) break;
      cin >> m;
      for(int i=0;i<n;i++) 
	for(int j=0;j<m;j++)
	  mincost[i][j] = (1<<29);  
      f = true;
      int s,t,mex = 0;
      scanf("%d",&s);
      for(int i=0;i<s;i++)
	{
	  int x,y;
	  scanf("%d %d",&x,&y);
	  x--,y--;
	  mincost[y][x] = 0;
	  dfs(x,y);
	}
      f = false;
      scanf("%d",&t);
      for(int i=0;i<t;i++)
	{   
	  int pre_mincost[n][m];
	  for(int j=0;j<n;j++)
	    for(int k=0;k<m;k++)
	      pre_mincost[j][k] = mincost[j][k],visited[j][k] = false;
	  int p,q;
	  scanf("%d %d",&p,&q);

	  cnt = 0,p--,q--;
	  mincost[q][p] = 0,visited[q][p] = true;
	  
	  dfs(p,q);
	  
	  mex = max(mex,cnt);
	  for(int j=0;j<n;j++)
	    for(int k=0;k<m;k++)
	      mincost[j][k] = pre_mincost[j][k];
	}
      cout << mex << endl;
    }
  return 0;
}

C++: #include<iostream>
#include<vector>
#include<queue>
#include<functional>

const int INF = 1 << 24;

struct P{
	int x, y;
};

typedef std::pair<P, int> State;

std::vector<P> getPointYouCanGo(int x, int y){
	if(y % 2 == 0){//even
			return {{x-1, y-1}, {x-1, y}, {x-1, y+1}, {x, y-1}, {x, y+1}, {x+1, y}};
	}else{//odd
		return {{x-1, y}, {x, y-1}, {x, y+1}, {x+1, y-1}, {x+1, y}, {x+1, y+1}};
	}
}

template<class T>
std::vector<T> filter(const std::vector<T> v, std::function<bool(T)> cond){
	std::vector<T> result;
	for(auto e : v){
		if(cond(e)){
			result.push_back(e);
		}
	}
	return result;
}

int map[2][100][100], m, n;

void initializeMap0(){
	for(int i=0;i<n;i++){
		for(int j=0;j<m;j++){
			map[0][i][j] = -1;
		}
	}
}

void createMap(int x, int y){
	std::queue<State> sv;
	map[0][x][y] = 0;
	sv.push(std::make_pair(P{x, y}, 0));
	
	while(!sv.empty()){
		State s = sv.front(); sv.pop();
		P begin_p = s.first;
		int count = s.second;

		std::vector<P> pv = filter<P>(getPointYouCanGo(begin_p.x, begin_p.y), [](P p) -> bool{
				return 0 <= p.x && p.x < n && 0 <= p.y && p.y < m;
			});

		for(const P p : pv){
			if(map[0][p.x][p.y] == -1){
				map[0][p.x][p.y] = count + 1;
				sv.push(std::make_pair(p, count+1));
			}
		}
	}
}

void update(){
	for(int i=0;i<n;i++){
		for(int j=0;j<m;j++){
			map[1][i][j] = std::min(map[1][i][j], map[0][i][j]);
		}
	}
}

int main(){
	int s, t;

	while(std::cin >> m >> n, m){
		for(int j=0;j<100;j++){
			for(int k=0;k<100;k++){
				map[1][j][k] = INF;
			}
		}

		std::cin >> s;
		for(int i=0;i<s;i++){
			int x, y;
			std::cin >> x >> y;
			initializeMap0();
			createMap(x-1, y-1);
			update();
		}

		int maximumBlocks = 0;
		std::cin >> t;
		for(int k=0;k<t;k++){
			int x, y, blocks = 0;
			std::cin >> x >> y;
			initializeMap0();
			createMap(x-1, y-1);
			for(int i=0;i<n;i++){
				for(int j=0;j<m;j++){
					if(map[0][i][j] < map[1][i][j] && map[1][i][j] != 0){//win
						blocks++;
					}
				}
			}
			maximumBlocks = std::max(maximumBlocks, blocks);
		}

		std::cout << maximumBlocks << std::endl;
	}
}