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)
	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)
		if now.Person.Distance() == 0 && ans > now.Turn {
			ans = now.Turn
		}
		if v, ok := memo[now.Person]; ok && v <= now.Turn {
			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)
			}
		}
	}
	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 <queue>
using namespace std;

const int INF = 1000000;
int H,W;
class Point{
public:
  int tx;
  int ty;
  int kx;
  int ky;
  void set(int a,int b,int c,int d){
    tx = a;
    ty = b;
    kx = c;
    ky = d;
  }
};

int is_out_of_area(int y,int x){
  return x < 1 || x > W || y < 1 || H > H;
}
int main(){
  char F[52][52];
  int D[52][52];
  
  int tx,ty,kx,ky;
  while(1){
    cin >> W >> H;
    if(W == 0 && H == 0)
    break;
    cin >> tx >> ty >> kx >> ky;
    
    for(int y=0;y<=H+1;y++){
      for(int x=0;x<=W+1;x++){
        F[y][x] = 1;
      }
    }
    for(int y=1;y<=H;y++){
      for(int x=1;x<=W;x++){
        D[y][x] = INF;
        int a;
        cin >> a;
        F[y][x] = a;
      }
    }
    
    queue<Point> qa;
    Point p;
    p.set(tx,ty,kx,ky);
    qa.push(p);
    D[p.ty][p.tx] = 0;
    while(!qa.empty()){
      p = qa.front();
      qa.pop();
      if(D[p.ty][p.tx] >= 100){
        cout << "NA" << endl;
        break;
      }
      if(p.tx == p.kx && p.ty == p.ky){
        cout << D[p.ty][p.tx] << endl;
        return 0;
      }
      
      if(D[p.ty-1][p.tx] == INF && D[p.ky+1][p.kx] == INF){
        if(is_out_of_area(p.ty-1,p.tx) == 0 || is_out_of_area(p.ky+1,p.kx) == 0){
          if(F[p.ty-1][p.tx] == 0 || F[p.ky+1][p.kx] == 0){
            Point q;
            q.set(p.tx,p.ty-1,p.kx,p.ky+1);
            qa.push(q);
            D[q.ty][q.tx] = D[p.ty][p.tx] + 1;
          }
        }
      }
      if(D[p.ty+1][p.tx] == INF && D[p.ky-1][p.kx] == INF){
        if(is_out_of_area(p.ty-1,p.tx) == 0 || is_out_of_area(p.ky+1,p.kx) == 0){
          if(F[p.ty+1][p.tx] == 0 || F[p.ky-1][p.kx] == 0){
            Point q;
            q.set(p.tx,p.ty+1,p.kx,p.ky-1);
            qa.push(q);
            D[q.ty][q.tx] = D[p.ty][p.tx] + 1;
          }
        }
      }
      if(D[p.ty][p.tx-1] == INF && D[p.ky][p.kx+1] == INF){
        if(is_out_of_area(p.ty,p.tx) == 0 || is_out_of_area(p.ky,p.kx) == 0){
          if(F[p.ty][p.tx-1] == 0 || F[p.ky][p.kx+1] == 0){
            Point q;
            q.set(p.tx-1,p.ty,p.kx+1,p.ky);
            qa.push(q);
            D[q.ty][q.tx] = D[p.ty][p.tx] + 1;
          }
        }
      }
      if(D[p.ty][p.tx+1] == INF && D[p.ky][p.kx-1] == INF){
        if(is_out_of_area(p.ty,p.tx+1) == 0 || is_out_of_area(p.ky,p.kx-1) == 0){
          if(F[p.ty][p.tx+1] == 0 || F[p.ky][p.kx-1] == 0){
            Point q;
            q.set(p.tx+1,p.ty,p.kx-1,p.ky);
            qa.push(q);
            D[q.ty][q.tx] = D[p.ty][p.tx] + 1;
          }
        }
      }
      
    }
    cout << "NA" << endl;
  }
  return 0;
}

C++: #include<iostream>
#include<utility>
#include<queue>
#include<map>
using namespace std;
int dx[4] = { 1,0,-1,0 };
int dy[4] = { 0,1,0,-1 };
int main() {
	int W, H, tx, ty, kx, ky;
	bool d[52][52];
	map<pair<pair<int, int>, pair<int, int> >,bool> m;
	pair<pair<int, int>, pair<int, int> >num;
	pair<pair<int, int>, pair<int, int> >copy;
	while (true) {
		cin >> W >> H;
		if (W == 0)break;
		for (int i = 0; i < H+2; i++) {
			for (int j = 0; j < W+2; j++) {
				d[i][j] = 1;
			}
		}
		cin >> tx >> ty >> kx >> ky;
		for (int i = 1; i < H + 1; i++) {
			for (int j = 1; j < W + 1; j++) {
				cin >> d[j][i];
			}
		}
		num.first.first = tx;
		num.first.second = ty;
		num.second.first = kx;
		num.second.second = ky;
		queue<pair<pair<int, int>, pair<int, int> > > q;
		q.push(num);
		int qsize = q.size();
		int loopcount = 0;
		while (!q.empty()) {
			num = q.front();
			q.pop();
			if (qsize == 0) {
				qsize = q.size()+1;
				loopcount++;
				if (loopcount == 100) {
					cout << "NA" << endl;
					break;
				}
			}
			qsize--;
			m[num] = true;
			swap(num.first, num.second);
			m[num] = true;
			if (num.first.first == num.second.first && num.first.second == num.second.second) {
				cout << loopcount << endl;
				break;
			}
			for (int i = 0; i < 4; i++) {
				if (!d[num.first.first + dx[i]][num.first.second + dy[i]]) {
					copy.first.first = num.first.first + dx[i];
					copy.first.second = num.first.second + dy[i];
				}
				if (!d[num.second.first - dx[i]][num.second.second - dy[i]]) {
					copy.second.first = num.second.first - dx[i];
					copy.second.second = num.second.second - dy[i];
				}
				if (!m[copy]) {
					q.push(copy);
				}
			}
			if (q.empty()) {
				cout << "NA" << endl;
			}
		}
	}
	return 0;
}