Go: package main

import (
	"fmt"
	"math"
)

type Position struct {
	X int64
	Y int64
}

func (one Position) Distance(another Position) int64 {
	return int64(math.Abs(float64(one.X-another.X)) + math.Abs(float64(one.Y-another.Y)))
}

type PersonPosition struct {
	Takayuki Position
	Kazuyuki Position
}

func (one PersonPosition) Distance() int64 {
	return one.Takayuki.Distance(one.Kazuyuki)
}

type Status struct {
	Person PersonPosition
	Turn   int64
}

type PQStatus []*Status

func solve(h, w int64) {
	var tx, ty, kx, ky int64
	fmt.Scan(&tx, &ty, &kx, &ky)
	tx--
	ty--
	kx--
	ky--
	m := make([][]int64, h)
	for i := range m {
		m[i] = make([]int64, w)
		for j := int64(0); j < w; j++ {
			fmt.Scan(&m[i][j])
		}
	}
	start := &Status{Person: PersonPosition{Takayuki: Position{X: tx, Y: ty}, Kazuyuki: Position{X: kx, Y: ky}}, Turn: 0}
	pq := make(PQStatus, 0)
	pq = append(pq, start)
	dx := []int64{0, 1, 0, -1}
	dy := []int64{1, 0, -1, 0}
	memo := make(map[PersonPosition]int64, 0)
	ans := int64(102)
	for len(pq) > 0 {
		now := pq[0]
		pq = pq[1:]
		if now.Person.Distance() == 0 && ans > now.Turn {
			ans = now.Turn
		}
		if ans <= now.Turn {
			continue
		}

		if _, ok := memo[now.Person]; ok {
			continue
		}
		memo[now.Person] = now.Turn

		for i := 0; i < 4; i++ {
			next := &Status{}
			*next = *now
			next.Person.Kazuyuki.X += dx[i]
			next.Person.Kazuyuki.Y += dy[i]
			if next.Person.Kazuyuki.X < 0 || next.Person.Kazuyuki.X >= w ||
				next.Person.Kazuyuki.Y < 0 || next.Person.Kazuyuki.Y >= h ||
				m[next.Person.Kazuyuki.Y][next.Person.Kazuyuki.X] == 1 {
				next.Person.Kazuyuki.X -= dx[i]
				next.Person.Kazuyuki.Y -= dy[i]
			}
			next.Person.Takayuki.X -= dx[i]
			next.Person.Takayuki.Y -= dy[i]
			if next.Person.Takayuki.X < 0 || next.Person.Takayuki.X >= w ||
				next.Person.Takayuki.Y < 0 || next.Person.Takayuki.Y >= h ||
				m[next.Person.Takayuki.Y][next.Person.Takayuki.X] == 1 {
				next.Person.Takayuki.X += dx[i]
				next.Person.Takayuki.Y += dy[i]
			}
			next.Turn++
			if next.Turn <= 100 {
				pq = append(pq, next)
			}
		}
	}
	if ans == 102 {
		fmt.Println("NA")
	} else {
		fmt.Println(ans)
	}
}

func main() {
	var h, w int64
	for {
		fmt.Scan(&h, &w)
		if h == 0 && w == 0 {
			break
		}
		solve(h, w)
	}
}

C++: #include <iostream>
#include <cstdio>
#include <cstdlib>
#include <math.h>
#include <vector>
#include <queue>
#include <algorithm>
#include <sstream>
#include <string>
using namespace std;
#define FOR(I,N) for(int I = 0; I < (int)(N); I++)
#define FIN(V) cout<<V<<endl
#define pb push_back
#define INF 100000
typedef pair<int, int> P;
int w, h, sx, sy, tx, ty, kx, ky;
bool maze[51][51];
int dx[4] = {0, 0, 1, -1};
int dy[4] = {1, -1, 0, 0};
int bfs();
int main(void){
    while(cin >> w >> h, w){
        if(h == 0 && w == 0)cout << "zero";
        cin >> tx >> ty;
        cin >> kx >> ky;
        fill_n(*maze, 51*51, 1);
        for(int i = 1; i <= h; i++){
            for(int j = 1; j <= w; j++){
                cin >> maze[i][j];
            }
        }
        int ans = bfs();
        if(ans == -1)FIN("NA");
        else FIN(ans);
    }
    return 0;
}

int bfs(){
int dk[51][51];
int dt[51][51];
    queue<P> quet;
    queue<P> quek;
    
    fill_n(*dk, 51*51, INF);
    fill_n(*dt, 51*51, INF);

    quet.push(P(tx, ty));
    quek.push(P(kx, ky));
    dt[ty][tx] = 0;
    dk[ky][kx] = 0;
    int cnt = 0;

    while(!quek.empty() || !quet.empty()){
        P pt = quet.front();
        P pk = quek.front();
        quet.pop();
        quek.pop();
        int now_tx = pt.first, now_ty = pt.second;
        int now_kx = pk.first, now_ky = pk.second;
        /*if(dt[now_ty][now_tx] >= 100 || dk[now_ky][now_kx] >= 100 || cnt >= 100){
            flag = false;
            //quek.clear();
            //quet.clear();
            return;
        }*/
        if(now_kx == now_tx && now_ky == now_ty){
            return max(dt[now_ty][now_tx], dk[now_ky][now_kx]);
        }
        FOR(i, 4){
            int move_tx = now_tx + dx[i];
            int move_ty = now_ty + dy[i];
            int move_kx = now_kx + (-dx[i]);
            int move_ky = now_ky + (-dy[i]);
            if(move_tx < 1 || move_tx > w)move_tx = now_tx;
            if(move_ty < 1 || move_ty > h)move_ty = now_ty;
            if(dt[now_ty][now_tx] >= 100 || dk[now_ky][now_kx] >= 100 || cnt >= 100){
                return -1;
            }
            //if(move_kx < 1 || move_kx > w)move_kx = now_kx;
            //if(move_ky < 1 || move_ky < h)move_ky = now_ky;
            //if(move_kx >= w || move_ky >= h || move_tx >= w || move_ty >= h)continue;
            if(maze[move_ty][move_tx] == 1 && maze[move_ky][move_kx] == 1)continue;
            if(dt[move_ty][move_tx] != INF && dk[move_ky][move_kx] != INF){cnt++;continue;};
            if(maze[move_ty][move_tx] != 1){// && dt[move_ty][move_tx] == INF){
                    quek.push(P(move_kx, move_ky));
                    quet.push(P(move_tx, move_ty));
                    dt[move_ty][move_tx] = dt[now_ty][now_tx] + 1;
                    dk[move_ky][move_kx] = dk[now_ky][now_kx] + 1;
            }
    }
}
return -1;

}

/*
   cout << "Km:" << i << endl;
            cout << "x:" << move_kx << " y:" << move_ky << endl;
            cout << "Tm:" << i << endl;
            cout << "x:" << move_tx << " y:" << move_ty << endl;
         
                 FOR(j,15){
            if(maze[u][j] == 1) cout << "# ";
            else if(dk[u][j] == INF && dt[u][j] == INF)cout << ". ";
            else if(dk[u][j] != INF)cout << dk[u][j]<< " ";
            else cout << dt[u][j]<<" ";
        }
        cout << endl;
*/

C++: #include<iostream>
#include<queue>
using namespace std;

bool went[50 + 10][50 + 10][50 + 10][50 + 10] = { 0 };

int map[50 + 10][50 + 10] = { 0 };

int gx[] = { 1,0,-1,0,-1,0,1,0 };
int gy[] = { 0,1,0,-1,0,-1,0,1 };

struct ST
{
	int tx, ty;
	int kx, ky;
	int tim=0;
};

bool ChekNow(ST);


ST GoMap(ST, int);


int main()
{
	ST now,tmp;

	queue <ST> nx;


	int w, h;
	int tsx, tsy;
	int ksx, ksy;

	bool flg;
	int i, j;

	while (cin >> w >> h, w != 0 && h != 0)
	{
		flg = true;

		cin >> tsx >> tsy;
		cin >> ksx >> ksy;
		
		for (i = 1; i <= h; i++)
		{
			map[i][0] = map[i][w + 1] = 1;

			for (j = 1; j <= w; j++)
			{
				cin >> map[i][j];
			}
		}

		for (i = 0; i <= w + 1; i++)
		{
			map[0][i] = 1;
			map[h + 1][i] = 1;
		}


		now.tx = tsx;
		now.ty = tsy;
		now.kx = ksx;
		now.ky = ksy;
		now.tim = 0;

		nx.push(now);

		while (!nx.empty() && tmp.tim<100)
		{
			now = nx.front();
			nx.pop();

			if (ChekNow(now))
			{
				continue;
			}
			went[now.tx][now.ty][now.kx][now.ky] = true;

			if (now.tx == now.kx && now.ty == now.ky)
			{
				cout << now.tim << endl;

				flg = false;

				break;
			}

			for (i = 0; i < 4; i++)
			{
				tmp=GoMap(now, i);

				if (!ChekNow(tmp))
				{
					tmp.tim++;
					nx.push(tmp);
				}
			}
		}

		if (flg)
		{
			cout << "NA\n";
		}

		while (!nx.empty())
		{
			nx.pop();
		}
	}
	return 0;
}


bool ChekNow(ST ex)
{
	return went[ex.tx][ex.ty][ex.kx][ex.ky];
}


ST GoMap(ST ex, int i)
{
	if (map[ex.ty + gy[i]][ex.tx + gx[i]] == 0)
	{
		ex.ty += gy[i];
		ex.tx += gx[i];
	}
	if (map[ex.ky + gy[i + 4]][ex.kx + gx[i + 4]] == 0)
	{
		ex.ky += gy[i + 4];
		ex.kx += gx[i + 4];
	}

	return ex;
}