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;
typedef pair<P,int> Pi;
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}};
 
void dfs(int x,int y)
{
 
  deque<Pi> deq;
  deq.push_back(Pi(P(x,y),0));
  mincost[y][x] = 0;
  visited[y][x] = true;
  cnt = 1;
  while(!deq.empty())
    {
      Pi pi = deq.front(); deq.pop_front();
 
      for(int i=0;i<6;i++)
    {
      int nx = pi.first.first + dx[pi.first.second%2][i];
      int ny = pi.first.second + dy[pi.first.second%2][i];
 
      if(!(0 <= nx && nx < m && 0 <= ny && ny < n))
        continue;
 
      if(mincost[ny][nx] > pi.second + 1)
        {
          if(!visited[ny][nx])
        cnt++;
          visited[ny][nx] = true;
          mincost[ny][nx] = pi.second + 1;
          deq.push_back(Pi(P(nx,ny),pi.second+1));
        }
    }
    }
}
 
int main()
{
  while(cin >> m >> n,m)
    {
      cerr << m << " " << n << endl;
      for(int i=0;i<n;i++) 
    for(int j=0;j<m;j++)
      mincost[i][j] = (1<<29);  
      
      int s,t,mex = 1;
      scanf("%d",&s);
      cerr << s << endl;
      for(int i=0;i<s;i++)
    {
      int x,y;
      scanf("%d %d",&x,&y);
      cerr << x << " " << y << endl;
      x--,y--;
      mincost[y][x] = 0;
      dfs(x,y);
    }
      
      scanf("%d",&t);
      cerr << t << endl;
      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);
      cerr << p << " " << q << endl;
      p--,q--;
      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 <cmath>
using namespace std;

#define ABS(n) (n<0?-(n):(n))

#define INF (1<<20)
int field[128][128];

int dist(int x1, int y1, int x2, int y2)
{
	x1-=(y1-1)/2;
	x2-=(y2-1)/2;

	return (abs(x1-x2)+abs(y1-y2)+abs((x1+y1)-(x2+y2)))/2;
}

int main()
{
	int w,h,n,x0,y0,cnt,ans;
	while(cin >> w, w)
	{
		cin >> h;
		for(int y=1; y<=h; y++)
		for(int x=1; x<=w; x++)
		{
			field[y][x] = INF;
		}
		
		cin >> n;
		while(n--)
		{
			cin >> x0 >> y0;
			for(int y=1; y<=h; y++)
			for(int x=1; x<=w; x++)
			{
				field[y][x] = min(field[y][x],dist(x0,y0,x,y));
			}
		}

		ans = 0;
		cin >> n;
		while(n--)
		{
			cnt = 0;
			cin >> x0 >> y0;
			for(int y=1; y<=h; y++)
			for(int x=1; x<=w; x++)
			{
				if(field[y][x]>dist(x0,y0,x,y)) cnt++;
			}
			ans = max(ans,cnt);
		}
		cout << ans << endl;
	}
	return 0;
}