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 <string>
#include <algorithm>
#include <cstring>
#include <queue>
using namespace std;

int X, Y;
int field[50][50];

bool visit[50][50][50][50];

struct Node {
	int takx, taky;
	int kazx, kazy;
	int turn;
	Node(int takx, int taky, int kazx, int kazy) : takx(takx), taky(taky), kazx(kazx), kazy(kazy), turn(0) {}

	bool isOk() {
		return takx == kazx && taky == kazy;
	}

	// right, up, left, down
	Node move(int dir) {
		static int dx[4] = {1, 0, -1, 0};
		static int dy[4] = {0, 1, 0, -1};
		Node next = *this;

		int nx, ny;

		nx = takx + dx[dir];
		ny = taky + dy[dir];

		if(0 <= nx && nx < X && 0 <= ny && ny < Y) {
			if(field[nx][ny] == 0) next.takx = nx, next.taky = ny;
		}

		nx = kazx + dx[(dir + 2) % 4];
		ny = kazy + dy[(dir + 2) % 4];

		if(0 <= nx && nx < X && 0 <= ny && ny < Y) {
			if(field[nx][ny] == 0) next.kazx = nx, next.kazy = ny;
		}

		next.turn++;
		return next;
	}
};

int main() {
	for(; cin >> X >> Y, X || Y;) {
		int tx, ty;
		int kx, ky;
		cin >> tx >> ty >> kx >> ky;
		tx--, ty--, kx--, ky--;

		memset(visit, 0, sizeof visit);
		memset(field, 0, sizeof field);

		visit[tx][ty][kx][ky] = true;

		for(int y = 0; y < Y; y++) {
			for(int x = 0; x < X; x++) {
				cin >> field[x][y];
			}
		}

		queue<Node> Q;
		Q.push(Node(tx, ty, kx, ky));

		int ans = -1;
		while(!Q.empty()) {
			Node node = Q.front(); Q.pop();
			if(node.turn >= 100) continue;
			if(node.isOk()) {
				ans = node.turn;
				break;
			}
			for(int i = 0; i < 4; i++) {
				Node next = node.move(i);
				if(!visit[next.takx][next.taky][next.kazx][next.kazy]) {
					visit[next.takx][next.taky][next.kazx][next.kazy] = true;
					Q.push(next);
				}
			}
		}

		if(ans == -1) cout << "NA" << endl;
		else cout << ans << endl;
	}
}