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 <vector>

using namespace std;

const int size = 31;

char map[size][size];
char map2[size][size];

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

int getDir(char c) {
  return c == 'N' ? 1
      : c == 'E' ? 0
      : c == 'W' ? 2
      : c == 'S' ? 3
      : -1;
}
char dirs[] = {'E', 'N', 'W', 'S'};

int main()
{
  int w, h;
  while(cin >> w >> h, w || h) {
    int numPeeps = 0;
    for (int i = 0; i < h; i++) {
      for (int j = 0; j < w; j++) {
        char c;
        cin >> c;
        int dir = getDir(c);
        if(dir != -1) {
          numPeeps++;
        }
        map[i][j] = c;
      }
    }
    int t;
    for (t = 0; t <= 180 && numPeeps > 0; t++) {
      for (int i = 1; i < h-1; i++) {
        for (int j = 1; j < w-1; j++) {
          int dir = getDir(map[i][j]);
          if (dir != -1) {
            for (int k = 0; k < 4; k++) {
              int nextX = j + dx[(dir+k+3)%4];
              int nextY = i + dy[(dir+k+3)%4];
              char nextC = map[nextY][nextX];
              if(nextC == '.' || nextC == 'X') {
                map[i][j] = dirs[(dir+k+3)%4];
                break;
              }
            }
          }
        }
      }
      for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
          map2[i][j] = map[i][j];
        }
      }

      for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
          if (map[i][j] != '.' && map[i][j] != 'X') continue;
          for (int k = 0; k < 4; k++) {
            int neibX = j + dx[k];
            int neibY = i + dy[k];
            if (neibX < 0 || w <= neibX || neibY < 0 || h <= neibY) continue;
            char neibC = map[neibY][neibX];
            int dir = getDir(neibC);
            if (dir == (k+2)%4) {
              if (map[i][j] == 'X') {
                map2[neibY][neibX] = '.';
                numPeeps--;
              }
              else {
                map2[i][j] = dirs[dir];
                map2[neibY][neibX] = '.';
              }
              break;
            }
          }
        }
      }
      for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
          map[i][j] = map2[i][j];
        }
      }
    }
    if (t <= 180) cout << t << endl;
    else cout << "NA" << endl;

  }
  return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <cfloat>
#include <ctime>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>

using namespace std;

#ifdef _MSC_VER
#define __typeof__ decltype

template <class T>
int __builtin_popcount(T n) { return n ? 1 + __builtin_popcount(n & (n - 1)) : 0; }
#endif

#define foreach(it, c) for (__typeof__((c).begin()) it=(c).begin(); it != (c).end(); ++it)
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define popcount __builtin_popcount

const double EPS = 1e-8;
typedef long long ll;
typedef pair<int, int> pint;

int main()
{
	int W, H;
	int dx[] = { 1, 0, -1, 0 };
	int dy[] = { 0, -1, 0, 1 };
	char* dirs = "ENWS";

	while (scanf("%d%d", &W, &H), W | H)
	{
		char maze[64][64];
		for (int i = 0; i < H; ++i)
			scanf("%s", maze + i);

		int time;
		for (time = 0; time < 180; ++time)
		{
			bool any = false;
			bool mark[64][64];
			memset(mark, 0, sizeof(mark));
			for (int i = 0; i < H; ++i)
			{
				for (int j = 0; j < W; ++j)
				{
					char* hoge = strchr(dirs, maze[i][j]);
					if (!hoge)
						continue;

					any = true;

					int dir = hoge - dirs;
					int next_dir = -1;
					for (int k = -1; k < 3; ++k)
					{
						int d = (dir + k + 4) % 4;
						int tx = j + dx[d];
						int ty = i + dy[d];
						if (tx < 0 || ty < 0 || tx >= W || ty >= H)
							continue;

						char c = maze[ty][tx];
						if (c == '.' || c == 'X')
						{
							next_dir = d;
							break;
						}
					}
					if (next_dir != -1)
					{
						maze[i][j] = dirs[next_dir];
						mark[i+dy[next_dir]][j+dx[next_dir]] = true;
					}
				}
			}
			if (!any)
				break;

			for (int i = 0; i < H; ++i)
			{
				for (int j = 0; j < W; ++j)
				{
					if (!mark[i][j])
						continue;

					int d;
					int tx, ty;
					for (d = 0; d < 4; ++d)
					{
						tx = j + dx[d];
						ty = i + dy[d];
						char* pp;
						if (tx >= 0 && ty >= 0 && tx < W && ty < H
							&& (pp = strchr(dirs, maze[i+dy[d]][j+dx[d]])) != NULL
							&& pp - dirs < 4 && maze[ty][tx] == dirs[(d+2)%4])
							break;
					}

					if (maze[i][j] == '.')
						swap(maze[i][j], maze[ty][tx]);
					else if (maze[i][j] == 'X')
						maze[ty][tx] = '.';
				}
			}
		}
		if (time != 180)
			printf("%d\n", time);
		else
			puts("NA");
	}

	return 0;
}