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 (pq PQStatus) Len() int {
	return len(pq)
}
func (pq PQStatus) Less(i, j int) bool {
	if pq[i].Turn == pq[j].Turn {
		return pq[i].Person.Distance() < pq[j].Person.Distance()
	}
	return pq[i].Turn < pq[j].Turn
}

func (pq PQStatus) Swap(i, j int) {
	pq[i], pq[j] = pq[j], pq[i]
}

func (pq *PQStatus) Push(x interface{}) {
	item := x.(*Status)
	*pq = append(*pq, item)
}

func (pq *PQStatus) Pop() interface{} {
	old := *pq
	n := len(old)
	item := old[n-1]
	*pq = old[0 : n-1]
	return item
}

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)
	//heap.Init(&pq)
	//heap.Push(&pq, start)
	//pq.Push(start)
	pq = append(pq, start)
	dx := []int64{0, 1, 0, -1}
	dy := []int64{1, 0, -1, 0}
	memo := make(map[PersonPosition]int64, 0)
	ans := int64(101)
	for pq.Len() > 0 {
		//now := heap.Pop(&pq).(*Status)
		//now := pq.Pop().(*Status)
		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 += 1
			if next.Turn <= 100 {
				//heap.Push(&pq, next)
				//pq.Push(next)
				pq = append(pq, next)
			}
		}
	}
	if ans == 101 {
		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 10000000
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};
void bfs();
bool flag = true;
int main(void){
    while(cin >> w >> h, w || h){
        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];
            }
        }
        bfs();
    }
    return 0;
}

void 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(cnt <= 100){
        P pt = quet.front();
        P pk = quek.front();
        if(maze[pt.second][pt.first] == 1){
            cout << "NA" << endl;
            break;
        }
        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){
            cout << max(dt[now_ty][now_tx], dk[now_ky][now_kx]) << endl;
            return;
        }
        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){
            flag = false;
            //quek.clear();
            //quet.clear();
            return;
        }
            //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;
            }
    }
}


}

/*
   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;
*/