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 <vector>
#include <algorithm>
using namespace std;

const int INF = 1 << 30;
const int dx[2][6] = { {0, -1, -1, -1, 0, 1}, {1, 0, -1, 0, 1, 1} };
const int dy[6] = {-1, -1, 0, 1, 1, 0};

class State
{
public:
  int x, y, c;
  State(int _x = 0, int _y = 0, int _c = 0)
    :x(_x), y(_y), c(_c) {}
};

int main()
{
  int m, n;
  while (cin >> m >> n) {
    if ((m|n) == 0)
      break;

    int s;
    cin >> s;
    vector<vector<int> > cost(n, vector<int>(m, INF));
    for (int i = 0; i < s; ++i) {
      int x, y;
      cin >> x >> y;
      queue<State> que;
      que.push(State(x-1, y-1));
      while (!que.empty()) {
	const State st = que.front();
	que.pop();

	if (cost[st.y][st.x] < st.c)
	  continue;

	cost[st.y][st.x] = st.c;
	for (int d = 0; d < 6; ++d) {
	  x = st.x + dx[st.y%2][d];
	  y = st.y + dy[d];
	  if (x < 0 || m <= x || y < 0 || n <= y || cost[y][x] < st.c+1)
	    continue;
	  cost[y][x] = st.c+1;
	  que.push(State(x, y, st.c+1));
	}
      }
    }

    int t;
    cin >> t;
    int ans = 0;
    for (int i = 0; i < t; ++i) {
      int x, y, cnt = 0;
      cin >> x >> y;
      queue<State> que;
      que.push(State(x-1, y-1));
      vector<vector<int> > visited(n, vector<int>(m, 0));
      while (!que.empty()) {
	const State st = que.front();
	que.pop();

	if (cost[st.y][st.x] <= st.c || visited[st.y][st.x])
	  continue;

	++cnt;
	visited[st.y][st.x] = 1;
	for (int d = 0; d < 6; ++d) {
	  x = st.x + dx[st.y%2][d];
	  y = st.y + dy[d];
	  if (x < 0 || m <= x || y < 0 || n <= y || cost[y][x] <= st.c+1 || visited[y][x])
	    continue;
	  que.push(State(x, y, st.c+1));
	}
      }
      ans = max(ans, cnt);
    }

    cout << ans << endl;
  }
  return 0;
}

C++: #include <iostream>
#include <vector>
#include <array>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <tuple>
#include <bitset>
#include <memory>
#include <cmath>
#include <algorithm>
#include <functional>
#include <iomanip>
#include <numeric>
#include <climits>
#include <cfloat>
#include <cassert>

struct HexCoordinate {
	int x, y;
	std::vector<HexCoordinate> neighbors() const {
		if (y % 2 == 0) {
			return { {x - 1, y}, {x + 1, y}, {x, y - 1}, {x + 1, y - 1}, {x, y + 1}, {x + 1, y + 1} };
		}
		else {
			return { {x - 1, y}, {x + 1, y}, {x - 1, y - 1}, {x, y - 1}, {x - 1, y + 1}, {x, y + 1} };
		}
	}
};
int main() {
	while (true) {
		int m, n; std::cin >> m >> n; if (n == 0 && m == 0) break;
		int s; std::cin >> s;
		std::vector<std::vector<int>> min_distance(n, std::vector<int>(m, INT_MAX));
		for (auto i = 0; i < s; ++i) {
			int x, y; std::cin >> x >> y;
			std::queue<HexCoordinate> queue; queue.push(HexCoordinate{ x, y });
			min_distance[y - 1][x - 1] = 0;
			while (!queue.empty()) {
				const auto top = queue.front(); queue.pop();
				for (const auto next : top.neighbors()) if (1 <= next.x && next.x <= m && 1 <= next.y && next.y <= n) {
					if (min_distance[next.y - 1][next.x - 1] > min_distance[top.y - 1][top.x - 1] + 1) {
						min_distance[next.y - 1][next.x - 1] = min_distance[top.y - 1][top.x - 1] + 1;
						queue.push(next);
					}
				}
			}
		}
		int t; std::cin >> t;
		int max_count = 0;
		for (auto i = 0; i < t; ++i) {
			int x, y; std::cin >> x >> y;
			auto min = min_distance;
			int count = 1;
			std::queue<HexCoordinate> queue; queue.push(HexCoordinate{ x, y });
			min[y - 1][x - 1] = 0;
			while (!queue.empty()) {
				const auto top = queue.front(); queue.pop();
				for (const auto next : top.neighbors()) if (1 <= next.x && next.x <= m && 1 <= next.y && next.y <= n) {
					if (min[next.y - 1][next.x - 1] > min[top.y - 1][top.x - 1] + 1) {
						min[next.y - 1][next.x - 1] = min[top.y - 1][top.x - 1] + 1;
						queue.push(next);
						++count;
					}
				}
			}
			max_count = std::max(max_count, count);
		}
		std::cout << max_count << '\n';
	}
}