Go: package main

import (
	"bufio"
	"os"
	"strconv"
	"strings"
	"fmt"
)

var scanner = bufio.NewScanner(os.Stdin)

type Point struct {
	x, y int
}

func main() {
	dx := []int{1, 0, -1, 0}
	dy := []int{0, -1, 0, 1}
	maze := make([][]rune, 30)
	for i := range maze {
		maze[i] = make([]rune, 30)
	}
	next := make([][]rune, 30)
	for i := range next {
		next[i] = make([]rune, 30)
	}
	check := make([][]int, 30)
	for i := range check {
		check[i] = make([]int, 30)
	}
	for scanner.Scan() {
		buf := strings.Split(scanner.Text(), " ")
		W, _ := strconv.Atoi(buf[0])
		H, _ := strconv.Atoi(buf[1])
		if W == 0 && H == 0 {
			break
		}
		for i := 0; i < H; i++ {
			scanner.Scan()
			buf_ := scanner.Text()
			for j, v := range buf_ {
				maze[i][j] = v
			}
		}
		man := 0
		for i := 0; i < H; i++ {
			for j := 0; j < H; j++ {
				if maze[i][j] != '.' && maze[i][j] != 'X' && maze[i][j] != '#' {
					switch maze[i][j] {
					case 'E':
						maze[i][j] = 0
						man++
					case 'N':
						maze[i][j] = 1
						man++
					case 'W':
						maze[i][j] = 2
						man++
					case 'S':
						maze[i][j] = 3
						man++
					}
				}
			}
		}
		ans := -1
		for t := 0; t <= 180; t++ {
			if man == 0 {
				ans = t
				break
			}
			for i := 0; i < H; i++ {
				for j := 0; j < W; j++ {
					check[i][j] = 0x7FFFFFFF
				}
			}
			for i := 0; i < H; i++ {
				for j := 0; j < W; j++ {
					if maze[i][j] > 3 {
						continue
					}
					l := (maze[i][j] + 3) % 4
					for k := 0; k < 4; k++ {
						y := i + dy[l]
						x := j + dx[l]
						if 0 <= y && y < H && 0 <= x && x < W && (maze[y][x] == '.' || maze[y][x] == 'X') {
							maze[i][j] = l
							check[y][x] = min(check[y][x], int((l+2)%4))
							break
						}
						l = (l + 1) % 4
					}
				}
			}
			for i := 0; i < H; i++ {
				for j := 0; j < W; j++ {
					next[i][j] = maze[i][j]
				}
			}
			for i := 0; i < H; i++ {
				for j := 0; j < W; j++ {
					if maze[i][j] > 3 {
						continue
					}
					y := i + dy[maze[i][j]]
					x := j + dx[maze[i][j]]
					if 0 <= y && y < H && 0 <= x && x < W && check[y][x] == int((maze[i][j]+2)%4) {
						if maze[y][x] == '.' {
							next[y][x] = maze[i][j]
						} else if maze[y][x] == 'X' {
							man--
						}
						next[i][j] = '.'
					}
				}
			}
			for i := 0; i < H; i++ {
				for j := 0; j < W; j++ {
					maze[i][j]=next[i][j]
				}
			}
		}
		if ^ans != 0 {
			fmt.Println(ans)
		} else {
			fmt.Println("NA")
		}
	}
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

C++: #include<iostream>
#include<set>
#include<map>
using namespace std;

typedef pair<int,int> P;

int dir(char a){
  if(a=='E')return 0;
  if(a=='N')return 1;
  if(a=='W')return 2;
  if(a=='S')return 3;
  return -1;
}

char inv_dir(int a){
  if(a==0)return 'E';
  if(a==1)return 'N';
  if(a==2)return 'W';
  return 'S';
}

int main(){
  int h,w;
  string grid[100];
  int dx[] = {1,0,-1,0},dy[] = {0,-1,0,1};

  while(cin >> w >> h && (w||h)){
    for(int i=0;i<h;i++)cin >> grid[i];

    int ans = 0;
    while(ans<=180){
      set<P> s;
      int num = 0;
      for(int i=0;i<h;i++){
	for(int j=0;j<w;j++){
	  int d = dir(grid[i][j]);
	  if(0<=d){
	    num++;
	    for(int k=-1;k<3;k++){
	      int dd = (d+k+4)%4;
	      int sy = i+dy[dd], sx = j+dx[dd];
	      if(sy<0 || sx<0 || h<=sy || w<=sx)continue;
	      if(grid[sy][sx] == '.' || grid[sy][sx] == 'X'){
		grid[i][j] = inv_dir(dd);
		s.insert(P(sy,sx));
		break;
	      }
	    }
	  }
	}
      }
      if(!num)break;
      set<P>::iterator ite;
      for(ite=s.begin();ite!=s.end();ite++){
	P p = *ite;
	for(int i=0;i<4;i++){
	  int sy = p.first+dy[i], sx = p.second+dx[i];
	  //if(sy<0 || sx<0 || h<=sy || w<=sx)continue;
	  int dd = (i+2)%4;
	  if(dir(grid[sy][sx])==dd){
	    grid[sy][sx] = '.';
	    if(grid[p.first][p.second]!='X')grid[p.first][p.second] = inv_dir(dd);
	    break;
	  }
	}
      }
      ans++;
      /*
      if(ans<10){
	cout << ans << endl;
	for(int i=0;i<h;i++)cout << grid[i] << endl;
	cout << endl;
      }
      */
    }
    if(ans>180)cout << "NA\n";
    else cout << ans << endl;
  }
}

C++: #include <stdio.h>
#include <string.h>
#include <algorithm>
#include <iostream>
#include <math.h>
#include <assert.h>
#include <vector>

using namespace std;
typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;
static const double EPS = 1e-9;
static const double PI = acos(-1.0);

#define REP(i, n) for (int i = 0; i < (int)(n); i++)
#define FOR(i, s, n) for (int i = (s); i < (int)(n); i++)
#define FOREQ(i, s, n) for (int i = (s); i <= (int)(n); i++)
#define FORIT(it, c) for (__typeof((c).begin())it = (c).begin(); it != (c).end(); it++)
#define MEMSET(v, h) memset((v), h, sizeof(v))

int w, h;
char field[100][100];
int pdir[110][110];
int mapto[300];
int mapfrom[300];
const int dx[4] = { 1, 0, -1, 0 };
const int dy[4] = { 0, -1, 0, 1 };

void PrintField() {
  REP(y, h) {
    printf("%s\n", field[y]);
  }
  puts("");
}

void Push(int nx, int ny, int dir) {
  if (dir == 2) { pdir[ny][nx] = dir; }
  if (pdir[ny][nx] == 2) { return; }
  if (dir == 3) { pdir[ny][nx] = dir; }
  if (pdir[ny][nx] == 3) { return; }
  if (dir == 0) { pdir[ny][nx] = dir; }
  if (pdir[ny][nx] == 0) { return; }
  if (dir == 1) { pdir[ny][nx] = dir; }
  if (pdir[ny][nx] == 1) { return; }
}

int Person() {
  int ret = 0;
  REP(y, h) {
    REP(x, w) {
      if (mapto[(int)field[y][x]] <= 3) { ret++; }
    }
  }
  return ret;
}

int main() {
  MEMSET(mapto, 0x0f);
  mapto[(int)'E'] = 0;
  mapto[(int)'N'] = 1;
  mapto[(int)'W'] = 2;
  mapto[(int)'S'] = 3;
  mapfrom[0] = 'E';
  mapfrom[1] = 'N';
  mapfrom[2] = 'W';
  mapfrom[3] = 'S';
  while (scanf("%d %d", &w, &h), w|h) {
    REP(y, h) {
      scanf("%s", field[y]);
    }
    REP(t, 181) {
      //PrintField();
      MEMSET(pdir, 0x0f);
      if (Person() == 0) {
        printf("%d\n", t);
        goto next;
      }
      REP(y, h) {
        REP(x, w) {
          int dir = mapto[(int)field[y][x]];
          if (dir <= 3) {
            REP(i, 4) {
              int ndir = (dir + i + 3) % 4;
              int nx = x + dx[ndir];
              int ny = y + dy[ndir];
              if (field[ny][nx] == '.' ||
                  field[ny][nx] == 'X') {
                field[y][x] = mapfrom[ndir];
                Push(nx, ny, ndir);
                break;
              }
            }
          }
        }
      }
      REP(y, h) {
        REP(x, w) {
          int dir = pdir[y][x];
          if (dir <= 3) {
            int px = x + dx[(dir + 2) % 4];
            int py = y + dy[(dir + 2) % 4];
            field[py][px] = '.';
            if (field[y][x] == '.') {
              field[y][x] = mapfrom[dir];
            }
          }
        }
      }
    }
    puts("NA");
next:;
  }
}