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 <vector>
#include <queue>
#include <cstring>

using namespace std;

typedef pair<int,int> pii;
int n,m;
int s,t;
pii ps[101];
// »ê¼êÌÀW©çêÔß¢RrjÖÌ£
int dists[101][101];
const int INF=1000000000;
pii cand[101];
bool used[101][101];
bool noSet[101][101];

const int dy[2][6]={{-1,-1,0,1,1,0},{-1,-1,0,1,1,0}};
const int dx[2][6]={{-1,0,1,0,-1,-1},{0,1,1,1,0,-1}};

int updateMinDist(int sx,int sy,bool isSearch=true){
    memset(used,0,sizeof(used));
    queue<pii> q[2];
    int cur=0;
    int nxt=1;
    int cnt=0;
    pii sp=pii(sy,sx);
    used[sp.first][sp.second]=true;
    int res=0;
    q[cur].push(sp);
    while(q[cur].size()){
        while(q[cur].size()){
            pii p=q[cur].front();q[cur].pop();
            if(isSearch)dists[p.first][p.second]=min(dists[p.first][p.second],cnt);
            else if(dists[p.first][p.second]>cnt)res++;
            for(int i=0;i<6;i++){
                int ny=dy[p.first%2][i]+p.first;
                int nx=dx[p.first%2][i]+p.second;
                if(ny>=0&&nx>=0&&ny<n&&nx<m&&!used[ny][nx]){
                    q[nxt].push(pii(ny,nx));
                    used[ny][nx]=true;
                }
            }
        }
        cnt++;
        swap(cur,nxt);
    }
    return res;
}

int main(){
    while(cin>>m>>n&&(m|n)){
        memset(noSet,0,sizeof(noSet));
        cin>>s;
        for(int i=0;i<101;i++)for(int j=0;j<101;j++)dists[i][j]=INF;
        for(int i=0;i<s;i++){
            cin>>ps[i].second>>ps[i].first;
            ps[i].second--;
            ps[i].first--;
            noSet[ps[i].first][ps[i].second]=true;
        }
        for(int k=0;k<s;k++)updateMinDist(ps[k].second,ps[k].first);
        cin>>t;
        for(int i=0;i<t;i++){
            cin>>cand[i].second>>cand[i].first;
            cand[i].second--;
            cand[i].first--;
        }
        int res=0;
        for(int i=0;i<t;i++){
            int cnt=0;
            cnt=updateMinDist(cand[i].second,cand[i].first,false);
            res=max(res,cnt);
        }
        cout<<res<<endl;
    }
    return 0;
}

C++: #include <iostream>
#include <sstream>
#include <fstream>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <algorithm>
#include <numeric>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <cmath>
using namespace std;

typedef pair <int, int> PII;
typedef PII Node;
typedef queue <Node> Queue;

typedef vector <int> VI;
typedef vector <VI> VVI;

int w, h;
const int inf = 1<<24;
const int odx[6] = { 0, 1, 1, 1, 0, -1 };
const int ody[6] = { -1, -1, 0, 1, 1, 0 };
const int edx[6] = { -1, 0, 1, 0, -1, -1 };
const int edy[6] = { -1, -1, 0, 1, 1, 0 };

int bfs( VVI& M, int X, int Y ) {
    int answer = 1;
    Queue Q;
    Node start( X, Y );
    Q.push( start );
    M[Y][X] = 0;
    /*
    while ( !Q.empty() ) {
        Node node = Q.front();
        Q.pop();

        int x = node.first;
        int y = node.second;

        for ( int i = 0; i < 6; i++ ) {
            int nx = x + ( y%2==0 ? edx[i] : odx[i] );
            int ny = y + ( y%2==0 ? edy[i] : ody[i] );
            if ( nx < 0 || nx >= w || ny < 0 || ny >= h ) continue;
            if ( M[y][x] + 1 >= M[ny][nx] ) continue;
            M[ny][nx] = M[y][x] + 1;
            Node nnode( nx, ny );
            Q.push( nnode );
            answer++;
        }
    }
    */
    return answer;
}

int main() {
    while ( cin >> w >> h ) {
        VVI M( h, VI( w, inf ) );

        int s;
        cin >> s;
        for ( int i = 0; i < s; i++ ) {
            int x, y;
            cin >> x >> y;
            x--;
            y--;
            bfs( M, x, y );
        }

        int answer = 0;
        VVI backup = M;
        int t;
        cin >> t;
        for ( int i = 0; i < t; i++ ) {
            M = backup;
            int x, y;
            cin >> x >> y;
            x--;
            y--;
            answer = max( answer, bfs( M, x, y ) );
        }

        cout << answer << endl;
    }
    return 0;
}