Mujin Contest 2017 B. Row to Column

题目大意

给一个$n imes n$的棋盘，上面有黑白，每次任意取一行一列，把列染成行的颜色，问最少多少次让棋盘全黑。

简要题解

全黑列不要动，那么非全黑列在构造出全黑行之前显然是不增不减的（除非你主动去染全黑的列），然后构造出一个全黑行，然后去染就好。

比赛时就是这么想的，然而构造全黑行时脑子进了点水。。

#include <bits/stdc++.h>
using namespace std;
namespace my_header {
#define pb push_back
#define mp make_pair
#define pir pair<int, int>
#define vec vector<int>
#define pc putchar
#define clr(t) memset(t, 0, sizeof t)
#define pse(t, v) memset(t, v, sizeof t)
#define bl puts("")
#define wn(x) wr(x), bl
#define ws(x) wr(x), pc(' ')
    const int INF = 0x3f3f3f3f;
    typedef long long LL;
    typedef double DB;
    inline char gchar() {
        char ret = getchar();
        for(; (ret == '
' || ret == '
' || ret == ' ') && ret != EOF; ret = getchar());
        return ret; }
    template<class T> inline void fr(T &ret, char c = ' ', int flg = 1) {
        for(c = getchar(); (c < '0' || '9' < c) && c != '-'; c = getchar());
        if (c == '-') { flg = -1; c = getchar(); }
        for(ret = 0; '0' <= c && c <= '9'; c = getchar())
            ret = ret * 10 + c - '0';
        ret = ret * flg; }
    inline int fr() { int t; fr(t); return t; }
    template<class T> inline void fr(T&a, T&b) { fr(a), fr(b); }
    template<class T> inline void fr(T&a, T&b, T&c) { fr(a), fr(b), fr(c); }
    template<class T> inline char wr(T a, int b = 10, bool p = 1) {
        return a < 0 ? pc('-'), wr(-a, b, 0) : (a == 0 ? (p ? pc('0') : p) : 
            (wr(a/b, b, 0), pc('0' + a % b)));
    }
    template<class T> inline void wt(T a) { wn(a); }
    template<class T> inline void wt(T a, T b) { ws(a), wn(b); }
    template<class T> inline void wt(T a, T b, T c) { ws(a), ws(b), wn(c); }
    template<class T> inline void wt(T a, T b, T c, T d) { ws(a), ws(b), ws(c), wn(d); }
    template<class T> inline T gcd(T a, T b) {
        return b == 0 ? a : gcd(b, a % b); }
    template<class T> inline T fpw(T b, T i, T _m, T r = 1) {
        for(; i; i >>= 1, b = b * b % _m)
            if(i & 1) r = r * b % _m;
        return r; }
};
using namespace my_header;

int a[555][555];

int main() {
#ifdef lol
    freopen("b.in", "r", stdin);
    freopen("b.out", "w", stdout);
#endif

    int n = fr(), c = n, t = 0;
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= n; ++j) {
            a[i][j] = gchar();
            if (a[i][j] == '#')
                t = 1;
        }
    if (!t) {
        puts("-1");
        return 0;
    }
    for (int i = 1; i <= n; ++i) {
        int flg = true;
        for (int j = 1; j <= n; ++j) {
            if (a[j][i] == '.')
                flg = false;
        }
        c -= flg;
    }
    int ans = 2 * n;
    for (int i = 1; i <= n; ++i) {
        int x = 0;
        for (int j = 1; j <= n; ++j)
            if (a[i][j] == '.')
                ++x;
        int flg = 1;
        for (int j = 1; j <= n; ++j)
            if (a[j][i] == '#')
                flg = 0;
        x += flg;
        ans = min(ans, x + c);
    }
    wt(ans);

    return 0;
}