Hello, I'm trying to solve ZOJ — Fire Net problem, reading the statement, it looks like a backtracking for all the possible locations for the guns, I'm doing int, check all possible combination of valid locations for the guns. I'm getting the right answers for the example case, but WA in the submission. Is this the right approach ?

#include <iostream>
#include <string>
#include <sstream>
#include <vector>
#include <set>
#include <map>
#include <list>
#include <queue>
#include <stack>
#include <memory>
#include <iomanip>
#include <functional>
#include <new>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <climits>
#include <cctype>
#include <ctime>

#define REP(i, n) for((i) = 0; i < n; i++)
#define FOR(i, a, n) for((i) = a; i < n; i++)
#define FORR(i, a, n) for((i) = a; i <= n; i++)
#define for_each(q, s) for(typeof(s.begin()) q=s.begin(); q!=s.end(); q++)
#define sz(n) n.size()
#define pb(n) push_back(n)
#define all(n) n.begin(), n.end()

using namespace std;

typedef long long ll;
typedef long double ld;

int a, b, i, j, k, n, ans;
char maze[10][10];

int rec(int i, int j, int now) {
    maze[i][j] = 'U';
    for(k = i + 1; k < n && maze[k][j] != 'X'; k++) maze[k][j] = 'P';
    for(k = i - 1; k >= 0 && maze[k][j] != 'X'; k--) maze[k][j] = 'P';
    for(k = j + 1; k < n && maze[i][k] != 'X'; k++) maze[i][k] = 'P';
    for(k = j - 1; k >= 0 && maze[i][k] != 'X'; k--) maze[i][k] = 'P';

    if(now > ans) {
        ans = now;
    }

    for(a = 0; a < n; a++) for(b = 0; b < n; b++) {
        if(maze[a][b] == '.') rec(a, b, now + 1);
    }

}

int main(void) {
    //freopen("i.in", "r", stdin);
    while(scanf("%d", &n) == 1 && n != 0) {
        REP(i, n) {
            scanf("%s", maze[i]);
        }
        ans = 0;
        REP(i, n) REP(j, n) {
            if(maze[i][j] == '.') {
                rec(i, j, 1);
            }
            REP(a, n) REP(b, n) if(maze[a][b] != 'X') maze[a][b] = '.';
        }
        printf("%d\n", ans);
    }
    return 0;
}