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<queue>
#include<algorithm>
#include<vector>
#include<map>
using namespace std;
typedef pair < int , int > Pi;
typedef pair < int , Pi > Pii;
#define fr first
#define sc second

int m, n, s;
int min_cost[100][100];
int dy[] = { -1, -1, 0, 1, 1, 0};
int dx[][6] = {{ -1, 0, 1, 0, -1, -1}, { 0, 1, 1, 1, 0, -1}};

bool isover(int y, int x){
  return y < 0 || y >= n || x < 0 || x >= m;
}

void bfs(queue< Pii >& que){
  while(!que.empty()){
    Pii p = que.front();
    que.pop();
    for(int i = 0 ; i < 6 ; i++ ){
      int ny = p.sc.fr + dy[i], nx = p.sc.sc + dx[p.sc.fr % 2][i];
      if(isover( ny, nx) || min_cost[ny][nx] < p.fr + 1) continue;
      que.push(Pii( p.fr + 1, Pi( ny, nx)));
      min_cost[ny][nx] = p.fr + 1;
    }
  }
}

int prebfs(int y, int x){
  int ret = 0;
  bool used[100][100] = {{}};
  queue< Pii > que;
  que.push(Pii( 0, Pi( y, x)));

  if(!min_cost[y][x]) return 0;

  while(!que.empty()){
    Pii p = que.front();
    que.pop();
    if(used[p.sc.fr][p.sc.sc]++) continue;
    ret++;
    for(int i = 0 ; i < 6 ; i++ ){
      int ny = p.sc.fr + dy[i], nx = p.sc.sc + dx[p.sc.fr % 2][i];
      if(isover( ny, nx) || min_cost[ny][nx] <= p.fr + 1) continue;

      que.push(Pii( p.fr + 1, Pi( ny, nx)));
    }
  }
  return ret;
}

int main(){
  while(cin >> m, m){
    queue< Pii > que;
    fill_n( *min_cost, 10000, 1 << 30);

    cin >> n >> s;

    for(int i = 0 ; i < s ; i++ ){
      int x, y;
      cin >> x >> y;
      que.push( Pii( 0, Pi( y - 1, x - 1)));
      min_cost[y - 1][x - 1] = 0;
    }
    bfs(que);

    int t, ret = 0;
    cin >> t;
    while(t--){
      int p, q;
      cin >> p >> q;
      ret = max( ret,prebfs( q - 1, p - 1));
    }
    cout << ret << endl;
  }
}

C++: #include<iostream>
#include<queue>
#define mp make_pair
using namespace std;
typedef pair<int, int> pii;//x, y
typedef pair<int, pii> piii;//cost, x, y
int dx[2][6] = {
  {0, 1, 0, -1, -1, -1},
  {1, 1, 1,  0, -1,  0}
};
int dy[2][6] = {
  {-1, 0, 1, 1, 0, -1},
  {-1, 0, 1, 1, 0, -1}
};
int grid[110][110];
int n, m, a;

int bfs(int grid[110][110], int sx, int sy){
  queue<piii> que;
  int ans = 1;
  grid[sy][sx] = 0;
  que.push(mp(0, mp(sx, sy)));
  while(!que.empty()){
    piii p = que.front();que.pop();
    int cost = p.first;
    int x    = p.second.first;
    int y    = p.second.second;
    for (int i = 0; i < 6; i++) {
      int nx = x + dx[y&1][i], ny = y + dy[y&1][i];
      if(0 <= ny && ny < n &&
         0 <= nx && nx < m &&
         grid[ny][nx] > cost + 1){
        ans++;
        grid[ny][nx] = cost + 1;
        que.push(mp(cost + 1, mp(nx, ny)));
      }
    }
  }
  // for (int i = 0; i < n; i++) {
  //   for (int j = 0; j < m; j++) {
  //     std::cout << grid[i][j] << " ";
  //   }
  //   std::cout << std::endl;
  // }
  // std::cout << std::endl;

  return ans;
}

int main(int argc, char *argv[]){
  while(cin >> m >> n, n){
    int ans = 0, t;
    cin >> a;
    int sx[a], sy[a];
    for (int i = 0; i < a; i++) {
      cin >> sx[i] >> sy[i];
      sx[i]--;sy[i]--;
    }
    cin >> t;
    int px[t], py[t];
    for (int i = 0; i < t; i++) {
      cin >> px[i] >> py[i];
      px[i]--;py[i]--;
    }
    
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        grid[i][j] = 1e8;
      }
    }
    
    for (int i = 0; i < a; i++) {
      bfs(grid, sx[i], sy[i]);
    }

    for (int i = 0; i < t; i++) {
      int tmp[110][110];
      
      for (int j = 0; j < n; j++) {
        for (int k = 0; k < m; k++) {
          tmp[j][k] = grid[j][k];
        }
      }
      
      ans = max(ans, bfs(tmp, px[i], py[i]));
    }
    std::cout << ans << std::endl;
  }
  return 0;
}