Referência para UVa 639 (Luiza)

#include <stdio.h>
#include <algorithm>
using namespace std;

char grid[5][5];
int maxR=0;
int n;

bool valid() {
    bool rook=false;

    for (int i=0; i<n; i++) {
        rook=false;

        for (int j=0; j<n; j++)
            if (grid[i][j]=='X') rook=false;
            else {
                if (grid[i][j]=='R') {
                    if (rook) return false;
                    else rook=true;
                }
            }
    }

    for (int j=0; j<n; j++) {
        rook=false;

        for (int i=0; i<n; i++)
            if (grid[i][j]=='X') rook=false;
            else {
                if (grid[i][j]=='R') {
                    if (rook) return false;
                    else rook=true;
                }
            }
    }

    return true;
}

int count() {
    int cnt=0;

    for (int i=0; i<n; i++)
        for (int j=0; j<n; j++)
            if (grid[i][j]=='R') cnt++;

    return cnt;
}
void place(int p) {
    if (p==16) {
        if (valid()) maxR=max(count(),maxR);
        return;
    }

    if (grid[p/4][p%4]=='.') {
        grid[p/4][p%4]='R';
        place(p+1);
        grid[p/4][p%4]='.';
    }
    place(p+1);
}

int main() {
    while (1) {
        scanf("%d", &n);
        if (!n) break;
        maxR=0;

        for (int i=0; i<n; i++)
            for (int j=0; j<n; j++)
                scanf(" %c", &grid[i][j]);

        place(0);
        printf("%d\n", maxR);
    }

    return 0;
}