Go: package main

import (
	"container/heap"
	"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)
	dx := []int64{0, 1, 0, -1}
	dy := []int64{1, 0, -1, 0}
	memo := make(map[PersonPosition]struct{}, 0)
	for pq.Len() > 0 {
		now := heap.Pop(&pq).(*Status)
		if now.Person.Distance() == 0 {
			fmt.Println(now.Turn)
			return
		}
		if _, ok := memo[now.Person]; ok {
			continue
		}
		memo[now.Person] = struct{}{}
		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)
			}
		}
	}
	fmt.Println("NA")
}

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

C++: #include <iostream>
#include <vector>
#include <queue>
#include <complex>

using namespace std;

#define INF 1 << 20

typedef complex<int> P;

struct point {
	P p1, p2;
	int step;

	point(P p1, P p2, int step) : p1(p1), p2(p2), step(step) { }
	point() { this -> p1 = this -> p2 = P(0, 0); this -> step = 0; }
};

bool step[50][50][50][50] = {0};

int main() {
	int W, H;
	while (cin >> W >> H, W || H) {
		int s1x, s1y; cin >> s1x >> s1y;
		int s2x, s2y; cin >> s2x >> s2y;

		int wall[50][50];
		for (int y = 0; y < H; ++y)
			for (int x = 0; x < W; ++x)
				cin >> wall[y][x];

		bool f = false;
		queue<point> que; que.push( point( P(s1x-1, s1y-1), P(s2x-1, s2y-1), 0 ) );
		queue<P> dirs; dirs.push( P(0, 0) );
		while ( !que.empty() ) {
			point p = que.front(); que.pop();
			P dir = dirs.front(); dirs.pop();

			p.p1 += dir, p.p2 -= dir;

			if (p.step > 100) continue;
			if (p.p1.real() < 0 || p.p1.real() >= W || p.p1.imag() < 0 || p.p1.imag() >= H) p.p1 -= dir;
			if (p.p2.real() < 0 || p.p2.real() >= W || p.p2.imag() < 0 || p.p2.imag() >= H) p.p2 += dir;
			if (wall[p.p1.imag()][p.p1.real()]) p.p1 -= dir;
			if (wall[p.p2.imag()][p.p2.real()]) p.p2 += dir;
			if (step[p.p1.real()][p.p1.imag()][p.p2.real()][p.p2.imag()]) continue;
			step[p.p1.real()][p.p1.imag()][p.p2.real()][p.p2.imag()] = true;

// cout << p.p1.real() << " " << p.p1.imag() << " " << p.p2.real() << " " << p.p2.imag() << endl;

			if (p.p1 == p.p2) {
				cout << p.step << endl;
				f = true;
				break;
			}

			++p.step;
			que.push(p); dirs.push( P(1, 0) );
			que.push(p); dirs.push( P(-1, 0) );
			que.push(p); dirs.push( P(0, 1) );
			que.push(p); dirs.push( P(0, -1) );
		}
		if (f) continue;
		cout << "NA" << endl;

	}
}

C++: #include<iostream>
#include<vector>

using namespace std;

const int vx1[]={0,1,0,-1},vy1[]={-1,0,1,0},
			vx2[]={0,-1,0,1},vy2[]={1,0,-1,0};
const int MAX=60,INF=1<<29;
int X,Y;
bool map[MAX][MAX];
int vtd[MAX][MAX][MAX][MAX];

bool IDDFS(int x1,int y1,int x2,int y2,int depth,int lim);

int main(){
	while(cin>>X>>Y && X && Y){
		int x1,y1,x2,y2;
		cin>>x1>>y1>>x2>>y2;
		for(int y=1; y<=Y; y++)for(int x=1; x<=X; x++)	cin>>map[x][y];
		int l=-1,r=101,mid=0;
		while(l+1<r){
			mid=(l+r)/2;
			for(int i=0; i<=X; i++)for(int j=0; j<=Y; j++)for(int k=0; k<=X; k++)for(int m=0; m<=Y; m++)vtd[i][j][k][m]=INF;
			vtd[x1][y1][x2][y2]=0;
			if(IDDFS(x1,y1,x2,y2,0,mid))	r=mid;
			else							l=mid;
		}
		if(r>100)	cout<<"NA"<<endl;
		else		cout<<r<<endl;
	}
	return 0;
}

bool IDDFS(int x1,int y1,int x2,int y2,int depth,int lim){
	if(depth>lim)			return false;
	if(x1==x2 && y1==y2)	return true;
	vtd[x1][y1][x2][y2]=depth;
	for(int i=0; i<4; i++){
		int xx1=max(1,min(X,x1+vx1[i])),yy1=max(1,min(Y,y1+vy1[i])),
				xx2=max(1,min(X,x2+vx2[i])),yy2=max(1,min(Y,y2+vy2[i]));
		if(map[xx1][yy1]){
			xx1=x1;	yy1=y1;
		}
		if(map[xx2][yy2]){
			xx2=x2;	yy2=y2;
		}
		if(vtd[xx1][yy1][xx2][yy2]<=depth+1)	continue;
		if(IDDFS(xx1,yy1,xx2,yy2,depth+1,lim))	return true;
	}
	return false;
}

C++: #include<iostream>
#include<queue>
using namespace std;
struct xy{
  int tx,ty;
  int kx,ky;
  int ti;
};
int x,y;
xy tk;
int m[51][51],vt[51][51]={},vk[51][51]={};
int dx[4]={1,0,-1,0},dy[4]={0,1,0,-1};

bool g(int a,int b){
  if(a<=0 || a>x || b<=0 || b>x) return 0;
  return 1;
}

int bfs(){
  queue<xy> q;
  xy t,tmp;
  int ta,tb,ka,kb,ans=10000,tim;
  q.push(tk);
  while(!q.empty()){
    t=q.front(),q.pop();
    for(int i=0;i<4;i++){
      ta=t.tx+dx[i],tb=t.ty+dy[i],ka=t.kx-dx[i],kb=t.ky-dy[i],tim=t.ti+1;
      if(g(ta,tb) || g(ka,kb)){
	if(vt[ta][tb]==2 && vt[ta][tb]==2)continue;
	if(m[ta][tb]==1) tmp.tx=t.tx,tmp.ty=t.ty;
	else if(vt[ta][tb]==0 && m[ta][tb]!=1)tmp.tx=ta,tmp.ty=tb,vt[ta][tb]=2;
	if(m[ta][tb]==1) tmp.kx=t.kx,tmp.ky=t.ky;
	else if(vk[ka][kb]==0 && m[ka][kb]!=1)tmp.kx=ka,tmp.ky=kb,vt[ta][tb]=2;
	tmp.ti=tim;
	if(tmp.ti==100) break;
	if(tmp.tx==tmp.kx && tmp.ky==tmp.ty){
	  if(ans>tmp.ti) ans=tmp.ti;
	  continue;
	}
	q.push(tmp);
      }
    }
  }
  return ans;
}

int main(){
  while(1){
    int ans;
    cin>>x>>y;
    if(x+y==0) break;
    cin>>tk.tx>>tk.ty>>tk.kx>>tk.ky;
    for(int i=1;i<=x;i++)
      for(int j=1;j<=y;j++) vt[i][j]=0,vk[i][j]=0;
    tk.ti=0;
    for(int i=1;i<=x;i++)
      for(int j=1;j<=y;j++)  cin>>m[i][j];
    ans=bfs();
    if(ans<100) cout<<ans<<endl;
    else cout<<"NA"<<endl;
  }
  
  return 0;
}