B.cpp

#include <bits/stdc++.h>
using namespace std;

//----------------------------------- DEBUG -----------------------------------
#define sim template < class c
#define ris return * this
#define dor > debug & operator <<
#define eni(x) sim > typename \
enable_if<sizeof dud<c>(0) x 1, debug&>::type operator<<(c i) {
sim > struct rge { c b, e; };
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c* x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
~debug() { cerr << endl; }
eni(!=) cerr << boolalpha << i; ris; }
eni(==) ris << range(begin(i), end(i)); }
sim, class b dor(pair < b, c > d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
sim dor(const c&) { ris; }
#endif
};
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
// debug & operator << (debug & dd, P p) { dd << "(" << p.x << ", " << p.y << ")"; return dd; }

//----------------------------------- END DEBUG --------------------------------

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    int n,m;
    cin >> n >> m;
    // white 0, black 1
    char grid[n][m];
    for(int i=0;i<n;i++) {
        for(int j=0;j<m;j++) {
            cin >> grid[i][j];
        }
    }

    int xmin, xmax, ymin, ymax;
    xmin = 1e9;
    xmax = -1;
    ymin = 1e9;
    ymax = -1;
    int side;
    int cnt = 0;
    for(int i=0;i<n;i++) {
        for(int j=0;j<m;j++) {
            if(grid[i][j] == 'B') {
                cnt++;
                xmin=min(xmin, i);
                xmax=max(xmax, i);
                ymin=min(ymin, j);
                ymax=max(ymax, j);
            }
        }
    }

    if(cnt == 0) {
        cout << 1 << '\n';
    }
    else {
        side = max(xmax - xmin + 1, ymax - ymin + 1);
        if(side > min(n,m)) {
            cout << -1 << '\n';
        }
        else {
            cout << side * side - cnt << '\n';
        }
    }
}