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 := &Status{}
		*now = *pq[0]
		pq = pq[1:]
		if ans <= now.Turn {
			continue
		}
		if _, ok := memo[now.Person]; ok {
			continue
		}
		memo[now.Person] = now.Turn

		if now.Person.Distance() == 0 && ans > now.Turn {
			ans = 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 <queue>
#include <map>
using namespace std;
 
class Point2{
public:
    int tx;
    int ty;
    int kx;
    int ky;
};
 
int mk(Point2 p)        // キーを生成
{
    return (((p.tx-1)*50+(p.ty-1))*50+(p.kx-1))*50+(p.ky-1);
}
 
int main()
{
    while(true){
        int W, H;
        cin >> W >> H;
 
        if(W==0 && H==0)
            break;
 
        Point2 p;
        cin >> p.tx >> p.ty;
        cin >> p.kx >> p.ky;
 
        int d[52][52];
        for(int y=0; y<=H+1; y++){
            for(int x=0; x<=W+1; x++){
                d[y][x] = 1;            // 番兵
            }
        }
 
        for(int y=1; y<=H; y++){
            for(int x=1; x<=W; x++){
                cin >> d[y][x];
            }
        }
 
        queue<Point2> que;        // キュー
        que.push(p);
 
        map<int, int> n;          // マップ（時間）
        n[mk(p)] = 0;
 
        while(true){
            if(que.empty()){            // 出会うことができない場合
                cout << "NA" << endl;
                break;
            }
 
            p = que.front();
            que.pop();
 
            if(n[mk(p)]>=100){       // 100以上の時間を要する場合
                cout << "NA" << endl;
                break;
            }
 
            if(p.tx==p.kx && p.ty==p.ky){       // 2人が出会う
                cout << n[mk(p)] << endl;
                break;
            }
 
            Point2 q;
 
            // 東
            q = p;
            if(d[q.ty][q.tx+1]==0){
                q.tx = q.tx+1;
            }
            if(d[q.ky][q.kx-1]==0){
                q.kx = q.kx-1;
            }
            if(n.find(mk(q))==n.end()){
                que.push(q);
                n[mk(q)] = n[mk(p)]+1;
            }
 
            // 西
            q = p;
            if(d[q.ty][q.tx-1]==0){
                q.tx = q.tx-1;
            }
            if(d[q.ky][q.kx+1]==0){
                q.kx = q.kx+1;
            }
            if(n.find(mk(q))==n.end()){
                que.push(q);
                n[mk(q)] = n[mk(p)]+1;
            }
 
            // 南
            q = p;
            if(d[q.ty+1][q.tx]==0){
                q.ty = q.ty+1;
            }
            if(d[q.ky-1][q.kx]==0){
                q.ky = q.ky-1;
            }
            if(n.find(mk(q))==n.end()){
                que.push(q);
                n[mk(q)] = n[mk(p)]+1;
            }
 
            // 北
            q = p;
            if(d[q.ty-1][q.tx]==0){
                q.ty = q.ty-1;
            }
            if(d[q.ky+1][q.kx]==0){
                q.ky = q.ky+1;
            }
            if(n.find(mk(q))==n.end()){
                que.push(q);
                n[mk(q)] = n[mk(p)]+1;
            }
        }
    }
 
    return 0;
}

C++: #include <iostream>
#include <stdio.h>
#include <sstream>
#include <string>
#include <vector>
#include <map>
#include <queue>
#include <algorithm>
#include <set>
#include <math.h>
#include <utility>
#include <stack>
#include <string.h>
#include <complex>
using namespace std;

const int INF = 1<<29;
const double EPS = 1e-8;
typedef vector<int> vec;
typedef pair<int,int> P;

const int dx[] = {0,0,1,-1};
const int dy[] = {1,-1,0,0};

struct node{
    int d,tx,ty,kx,ky;
};

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

void print(node& p){
    for(int i=0;i<Y;i++){
        for(int j=0;j<X;j++){
            if(i==p.ty&&j==p.tx) cout << 't';
            else if(i==p.ky&&j==p.kx) cout << 'k';
            else cout << field[i][j];
        }
        cout << endl;
    }
    cout << endl;
}

int main(){
    while(1){
        scanf("%d%d",&X,&Y);
        if(!X)break;

        int tx,ty,kx,ky;
        scanf("%d%d%d%d",&tx,&ty,&kx,&ky);
        tx--;ty--;kx--;ky--;

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

        for(int i=0;i<Y;i++){
            for(int j=0;j<X;j++){
                for(int k=0;k<Y;k++){
                    for(int l=0;l<X;l++){
                        d[i][j][k][l] = INF;
                    }
                }
            }
        }

        queue<node> que;
        d[tx][ty][kx][ky] = 0;
        que.push((node){0,tx,ty,kx,ky});
        bool not_reach = true;
        while(que.size()){
            node p = que.front(); que.pop();
            if(p.d>=100)break;
            if(p.tx==p.kx&&p.ty==p.ky){
                cout << p.d << endl;
                not_reach = false;
                break;
            }
            for(int i=0;i<4;i++){
                int n_tx = p.tx+dx[i], n_ty = p.ty+dy[i];
                int n_kx = p.kx-dx[i], n_ky = p.ky-dy[i];
                if(n_tx<0||X<=n_tx||n_ty<0||Y<=n_ty||field[n_ty][n_tx]){
                    n_tx = p.tx; n_ty = p.ty;
                }
                if(n_kx<0||X<=n_kx||n_ky<0||Y<=n_ky||field[n_ky][n_kx]){
                    n_kx = p.kx; n_ky = p.ky;
                }
                if(d[n_tx][n_ty][n_kx][n_ky]>p.d+1){
                    d[n_tx][n_ty][n_kx][n_ky] = p.d+1;
                    que.push((node){p.d+1,n_tx,n_ty,n_kx,n_ky});
                }
            }
        }
        if(not_reach)cout << "NA" << endl;
    }
    return 0;
}