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| #include <bits/stdc++.h>
using namespace std;
struct Dinic {
struct Edge { int to, cap, rev; };
int N;
vector<vector<Edge>> G;
vector<int> level, it;
Dinic(int n=0) { init(n); }
void init(int n) { N = n; G.assign(n, {}); }
void add_edge(int u, int v, int c) {
Edge a{v, c, (int)G[v].size()};
Edge b{u, 0, (int)G[u].size()};
G[u].push_back(a); G[v].push_back(b);
}
bool bfs(int s, int t) {
level.assign(N, -1);
queue<int> q; level[s] = 0; q.push(s);
while (!q.empty()) {
int u = q.front(); q.pop();
for (auto &e : G[u]) if (e.cap > 0 && level[e.to] < 0) {
level[e.to] = level[u] + 1; q.push(e.to);
}
}
return level[t] >= 0;
}
int dfs(int u, int t, int f) {
if (u == t) return f;
for (int &i = it[u]; i < (int)G[u].size(); ++i) {
auto &e = G[u][i];
if (e.cap > 0 && level[u] + 1 == level[e.to]) {
int ret = dfs(e.to, t, min(f, e.cap));
if (ret > 0) { e.cap -= ret; G[e.to][e.rev].cap += ret; return ret; }
}
}
return 0;
}
long long max_flow(int s, int t) {
long long flow = 0;
while (bfs(s, t)) {
it.assign(N, 0);
while (true) {
int pushed = dfs(s, t, INT_MAX);
if (!pushed) break;
flow += pushed;
}
}
return flow;
}
};
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int T;
if (!(cin >> T)) return 0;
while (T--) {
int n, m; cin >> n >> m;
vector<string> g(n);
for (int i = 0; i < n; ++i) cin >> g[i];
auto inb = [&](int r, int c){ return 0 <= r && r < n && 0 <= c && c < m; };
vector<vector<int>> whiteId(n, vector<int>(m, -1));
vector<vector<int>> bVertId(n, vector<int>(m, -1));
vector<vector<int>> bHorizId(n, vector<int>(m, -1));
int W = 0, B = 0;
for (int i = 0; i < n; ++i)
for (int j = 0; j < m; ++j) {
if (g[i][j] == 'W') ++W;
else if (g[i][j] == 'B') ++B;
}
if (W != 2 * B) { cout << "NO\n"; continue; }
// Early infeasibility: each black needs at least one vertical and one horizontal white neighbor
bool ok = true;
for (int i = 0; i < n && ok; ++i)
for (int j = 0; j < m && ok; ++j)
if (g[i][j] == 'B') {
bool hasV = false, hasH = false;
if (inb(i-1,j) && g[i-1][j] == 'W') hasV = true;
if (inb(i+1,j) && g[i+1][j] == 'W') hasV = true;
if (inb(i,j-1) && g[i][j-1] == 'W') hasH = true;
if (inb(i,j+1) && g[i][j+1] == 'W') hasH = true;
if (!hasV || !hasH) ok = false;
}
if (!ok) { cout << "NO\n"; continue; }
// Assign ids
int wid = 0, bidV = 0, bidH = 0;
for (int i = 0; i < n; ++i)
for (int j = 0; j < m; ++j)
if (g[i][j] == 'W') whiteId[i][j] = wid++;
for (int i = 0; i < n; ++i)
for (int j = 0; j < m; ++j)
if (g[i][j] == 'B') {
bVertId[i][j] = bidV++;
bHorizId[i][j] = bidH++;
}
// Build flow network
// Nodes: S | Bv | Bh | W | T
int S = 0;
int offsetBv = 1;
int offsetBh = offsetBv + bidV;
int offsetW = offsetBh + bidH;
int Tt = offsetW + wid;
Dinic dinic(Tt + 1);
// S -> Bv, S -> Bh
for (int i = 0; i < n; ++i)
for (int j = 0; j < m; ++j)
if (g[i][j] == 'B') {
dinic.add_edge(S, offsetBv + bVertId[i][j], 1);
dinic.add_edge(S, offsetBh + bHorizId[i][j], 1);
}
auto addIfWhite = [&](int r, int c, int fromNode){
if (inb(r,c) && g[r][c] == 'W') {
dinic.add_edge(fromNode, offsetW + whiteId[r][c], 1);
}
};
// Bv -> W (vertical neighbors), Bh -> W (horizontal neighbors)
for (int i = 0; i < n; ++i)
for (int j = 0; j < m; ++j)
if (g[i][j] == 'B') {
int vNode = offsetBv + bVertId[i][j];
int hNode = offsetBh + bHorizId[i][j];
addIfWhite(i-1, j, vNode);
addIfWhite(i+1, j, vNode);
addIfWhite(i, j-1, hNode);
addIfWhite(i, j+1, hNode);
}
// W -> T
for (int i = 0; i < n; ++i)
for (int j = 0; j < m; ++j)
if (g[i][j] == 'W') {
dinic.add_edge(offsetW + whiteId[i][j], Tt, 1);
}
long long flow = dinic.max_flow(S, Tt);
cout << (flow == W ? "YES" : "NO") << "\n";
}
return 0;
}
|