UVa 639 Don't Get Rooked

/*
coder: ACboy
date: 2010-3-19
result: 1A
description: UVa 639 Don't Get Rooked
*/

#include <iostream>
using namespace std;

char chess[4][4];
char tempChess[4][4];
int everyPos[70000][16];
int c;

// 保存每个子集
void print_subset(int n, int s)
{
for (int i = 0; i < n; i++) {
if (s & (1 << i)) everyPos[c][i] = 1;
else everyPos[c][i] = 0;
}
c++;
}

// 生成所有的子集
void findAllPos(int n) {
for (int i = 0; i < 1 << n; i++) {
print_subset(n, i);
}
}

// 检查某一个位置上是否可以放车
int checkRowColumn(int row, int column, int n) {
int i;
int ok = 1;
for (i = column - 1; i >= 0 && tempChess[row][i] != 'X'; i--) {
if (tempChess[row][i] == '*') {
ok = 0;
break;
}
}
if (ok == 0) return 0;

for (i = column + 1; i < n && tempChess[row][i] != 'X'; i++) {
if (tempChess[row][i] == '*') {
ok = 0;
break;
}
}
if (ok == 0) return 0;

for (i = row - 1; i >= 0 && tempChess[i][column] != 'X'; i--) {
if (tempChess[i][column] == '*') {
ok = 0;
break;
}
}
if (ok == 0) return 0;

for (i = row + 1; i < n && tempChess[i][column] != 'X'; i++) {
if (tempChess[i][column] == '*') {
ok = 0;
break;
}
}
if (ok == 0) return 0;
return 1;
}

int checkLegal(int k, int n) {
int count = 0;
int i;
int row;
int column;
// 对每种可能先把所有的车放到棋盘上，并记录车的个数count
for (i = 0; i < n * n; i++) {
row = i / n;
column = i % n;
if (everyPos[k][i] == 1 && tempChess[row][column] == '.') {
count++;
tempChess[row][column] = '*';
}
}

// 检查每个车的位置是否合法，如果每个车的位置都合法，则得到一个解
int ok = 1;
for (i = 0; i < n * n; ++i) {
row = i / n;
column = i % n;
if (tempChess[row][column] == '*' && checkRowColumn(row, column, n) == 0) {
ok = 0;
break;
}
}
// 如果所有车的位置都合法则返回车的个数
if (ok) {
return count;
} else {
return 0;
}
}

int main()
{
int n;
#ifndef ONLINE_JUDGE
freopen("639.txt", "r", stdin);
#endif
while (cin >> n) {
if (n == 0) break;
int i, j;
for (i = 0; i < n; i++) {
for (j = 0; j < n; j++) {
cin >> chess[i][j];
}
}
c = 0;
findAllPos(n * n);
int max = -1;
for (i = 0; i < c; i++) {
memcpy(tempChess, chess, sizeof(chess));
int temp = checkLegal(i, n);
if (temp > max) max = temp;
}
cout << max << endl;
}
return 0;
}