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<bits/stdc++.h>
#define rep(i,n)for(int i=0;i<(n);i++)
using namespace std;

struct st { int x, y, c; };
int d[100][100], b[100][100], x[11], y[11];
int dx[][6]{ { 0,-1,0,1,1,1, },{ -1,-1,-1,0,1,0 } };
int dy[]{ -1,0,1,1,0,-1 };
int main() {
	int m, n, s;
	while (scanf("%d%d", &m, &n), m) {
		scanf("%d", &s);
		rep(i, s)scanf("%d%d", &x[i], &y[i]), x[i]--, y[i]--;
		int t; scanf("%d", &t);
		int Max = 0;
		rep(i, t) {
			scanf("%d%d", &x[s], &y[s]); x[s]--; y[s]--;
			queue<st>que;
			memset(d, -1, sizeof(d));
			rep(j, s + 1) {
				d[x[j]][y[j]] = 0; b[x[j]][y[j]] = j;
				que.push({ x[j],y[j],j });
			}
			while (!que.empty()) {
				st p = que.front(); que.pop();
				rep(j, 6) {
					int nx = p.x + dx[!(p.y & 1)][j], ny = p.y + dy[j];
					if (0 <= nx&&nx < m && 0 <= ny&&ny < n) {
						if (d[nx][ny] == -1) {
							d[nx][ny] = d[p.x][p.y] + 1;
							b[nx][ny] = p.c;
							que.push({ nx,ny,p.c });
						}
						else if (d[nx][ny] == d[p.x][p.y] + 1&&b[nx][ny]!=p.c) {
							b[nx][ny] = -1;
							que.push({ nx,ny,p.c });
						}
					}
				}
			}
			int cnt = 0;
			rep(i, m)rep(j, n) {
				if (b[i][j] == s)cnt++;
			}
			Max = max(Max, cnt);
		}
		printf("%d\n", Max);
	}
}

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,s,cnt;
int Cost[10][100][100];
int mincost[100][100];
bool visited[100][100];
int dx[2][6] = {{-1, -1, 0, 1, 0, -1}, {-1, 0, 1, 1, 1, 0}};
int dy[2][6] = {{0, -1, -1, 0, 1, 1},{0, -1, -1, 0, 1, 1}};

void dfs(int p,int x,int y,int cost)
{
  for(int i=0;i<6;i++)
    {
      int nx = x + dx[y%2][i];
      int ny = y + dy[y%2][i];
      if(!(0 <= nx && nx < m && 0 <= ny && ny < n))
	continue;

      if(Cost[p][ny][nx] > cost)
	{
	  Cost[p][ny][nx] = cost;
	  dfs(p,nx,ny,cost+1);
	}
    }
}

void dfs2(int x,int y,int cost)
{
  for(int i=0;i<6;i++)
    {
      int nx = x + dx[y%2][i];
      int ny = y + dy[y%2][i];
   
      if(!(0 <= nx && nx < m && 0 <= ny && ny < n))
	continue;

      if(mincost[ny][nx] <= cost)
	continue;    

      mincost[ny][nx] = cost;


      bool ok = true;
      for(int j=0;j<s;j++)
	if(Cost[j][ny][nx] <= cost)
	  {
	    ok = false;
	    break;
	  }

      if(ok)
	{
	  if(!visited[ny][nx])
	    cnt++;
	  visited[ny][nx] = true;
	  dfs2(nx,ny,cost+1);
	}
    }

}

int main()
{
  while(true)
    {
      cin >> n;
      if(!n)
	break;
      cin >> m;
    
      for(int i=0;i<10000000;i++);
      scanf("%d",&s);


      for(int i=0;i<s;i++)
	for(int j=0;j<n;j++)
	  for(int k=0;k<m;k++)
	    Cost[i][j][k] = (1<<29);
      
      for(int i=0;i<s;i++)
	{
	  int x,y;
	  scanf("%d %d",&x,&y);
	  x--,y--;
	  Cost[i][y][x] = 0;
	  dfs(i,x,y,1);
	}

      int t;
      scanf("%d",&t);

      int mex = 0;
      for(int i=0;i<t;i++)
	{
	  int p,q;
	  scanf("%d %d",&p,&q);
	  cnt = 1;
	  p--,q--;
	  
	  for(int j=0;j<n;j++)
	    for(int k=0;k<m;k++)
	      mincost[j][k] = (1<<29),visited[j][k] = false;
	  mincost[q][p] = 0;
	  visited[q][p] = true;
	  dfs2(p,q,1);
	  
	  mex = max(mex,cnt);
	}
      cout << mex << endl;

    }
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

const int dx[7] = {0, 0, -1, -1, 0, 1, 1};
const int dy[2][7] = {
	{0, -1, -1, 0, 1, 0, -1},
	{0, -1, 0, 1, 1, 1, 0}
};

int n, m;
int g[100][100];
int grid[100][100];
int grid2[100][100];

bool ok(int i, int j)
{
	return i >= 0 && j >= 0 && i < n && j < m;
}

int solve()
{
	int maxi = 0;
	memcpy(grid, g, sizeof(g));
	for (int a = 0; a < 100; a++){
		memset(grid2, 0, sizeof(grid2));
		for (int i = 0; i < n; i++){
			for (int j = 0; j < m; j++){
				for (int dir = 0; dir < 7; dir++){
					int nx = i + dx[dir];
					int ny = j + dy[i % 2][dir];
					if (!ok(nx, ny)) continue;
					grid2[nx][ny] |= grid[i][j];
				}
			}
		}
		
		memset(grid, 0, sizeof(grid));
		int cnt = 0;
		for (int i = 0; i < n; i++){
			for (int j = 0; j < m; j++){
				if (grid2[i][j] == (grid2[i][j] & (-grid2[i][j]))){
					grid[i][j] = grid2[i][j];
					if (grid[i][j] == 1) cnt++;
				}
				//printf("%d ", grid2[i][j]);
			}
			//puts("");
		}
		maxi = max(maxi, cnt);
	}
	return maxi;
}

int main()
{
	while (scanf("%d %d", &m, &n), m){
		memset(g, 0, sizeof(g));
		int maxi = 0;
		int s;
		scanf("%d", &s);
		for (int i = 0; i < s; i++){
			int x, y;
			scanf("%d %d", &x, &y);
			g[--y][--x] = 1 << i + 1;
		}
		int t;
		scanf("%d", &t);
		for (int i = 0; i < t; i++){
			int p, q;
			scanf("%d %d", &p, &q);
			g[--q][--p] = 1;
			maxi = max(maxi, solve());
			g[q][p] = 0;
		}
		printf("%d\n", maxi);
	}
	
	return 0;
}