Go: package main

import (
	"fmt"
	"math"
	"container/heap"
)

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 ans <= now.Turn {
			continue
		}
		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)
	}
}

Python: # from line_profiler import LineProfiler
from collections import deque
from sys import stdin

def main():
    while(True):
        W, H = map(int, stdin.readline().split())
        if not W: break
        tx,ty = map(int, stdin.readline().split())
        kx,ky = map(int, stdin.readline().split())
        ma = [[False]*(W+2) for _ in range(H+2)]
        for i in range(1,H+1):
            for j,a in enumerate(stdin.readline().split()):
                ma[i][j+1] = bool(1-int(a))
        que = deque([[tx,ty,kx,ky,0]])
        pas = set()
        ans = "NA"
        while(que):
            tx,ty,kx,ky,c = que.popleft()
            if c > 100: break
            if tx == kx and ty == ky:
                ans = c
                break
            for dx,dy in [[-1,0],[0,-1],[1,0],[0,1]]:
                tdx, tdy = [ dx, dy] if ma[ty+dy][tx+dx] else [0,0]
                kdx, kdy = [-dx,-dy] if ma[ky-dy][kx-dx] else [0,0]
                if (tx+tdx,ty+tdy,kx+kdx,ky+kdy) in pas: continue
                que.append([tx+tdx,ty+tdy,kx+kdx,ky+kdy,c+1])
                pas.add((tx+tdx,ty+tdy,kx+kdx,ky+kdy))
        print(ans)

if __name__ == "__main__":
    # prf = LineProfiler()
    # prf.add_function(main)
    # prf.runcall(main)
    # prf.print_stats()
    main()

Python: # from line_profiler import LineProfiler
from collections import deque
from sys import stdin

def main():
    while(True):
        W, H = map(int, stdin.readline().split())
        if not W: break
        tx,ty = map(int, stdin.readline().split())
        kx,ky = map(int, stdin.readline().split())
        ma = [[False]*(W+2) for _ in range(H+2)]
        for i in range(1,H+1):
            for j,a in enumerate(stdin.readline().split()):
                ma[i][j+1] = bool(1-int(a))
        que = deque([[tx,ty,kx,ky,0]])
        pas = set()
        ans = "NA"
        while(que):
            tx,ty,kx,ky,c = que.popleft()
            if not(tx-kx or ty-ky):
                ans = c
                break
            for dx,dy in [[-1,0],[0,-1],[1,0],[0,1]]:
                tdx, tdy = [ dx, dy] if ma[ty+dy][tx+dx] else [0,0]
                kdx, kdy = [-dx,-dy] if ma[ky-dy][kx-dx] else [0,0]
                if (tx+tdx,ty+tdy,kx+kdx,ky+kdy) in pas: continue
                if c+1 > 100: continue
                que.append([tx+tdx,ty+tdy,kx+kdx,ky+kdy,c+1])
                pas.add((tx+tdx,ty+tdy,kx+kdx,ky+kdy))
        print(ans)

if __name__ == "__main__":
    # prf = LineProfiler()
    # prf.add_function(main)
    # prf.runcall(main)
    # prf.print_stats()
    main()

Python: # from line_profiler import LineProfiler
from collections import deque
from sys import stdin

def main():
    while(True):
        W, H = map(int, stdin.readline().split())
        if not W: break
        tx,ty = map(int, stdin.readline().split())
        kx,ky = map(int, stdin.readline().split())
        ma = [[False]+[bool(1-int(a)) for a in stdin.readline().split()]+[False] for i in range(H)]
        ma = [[False]*(W+2)] + ma + [[False]*(W+2)]
        que = deque([[tx,ty,kx,ky,0]])
        pas = set()
        ans = "NA"
        while(que):
            tx,ty,kx,ky,c = que.popleft()
            if tx == kx and ty == ky:
                ans = c
                break
            if c+1 > 100: continue
            for dx,dy in [[-1,0],[0,-1],[1,0],[0,1]]:
                tdx, tdy = ( dx, dy) if ma[ty+dy][tx+dx] else (0,0)
                kdx, kdy = (-dx,-dy) if ma[ky-dy][kx-dx] else (0,0)
                if (tx+tdx,ty+tdy,kx+kdx,ky+kdy) in pas: continue
                que.append([tx+tdx,ty+tdy,kx+kdx,ky+kdy,c+1])
                pas.add((tx+tdx,ty+tdy,kx+kdx,ky+kdy))
        print(ans)

if __name__ == "__main__":
    # prf = LineProfiler()
    # prf.add_function(main)
    # prf.runcall(main)
    # prf.print_stats()
    main()