Index: lib/numeric/linearEq.cpp
==================================================================
--- lib/numeric/linearEq.cpp
+++ lib/numeric/linearEq.cpp
@@ -36,5 +36,7 @@
 			A[j] -= A[i] * r;
 		}
 	}
 	return A;
 }
+
+

ADDED   lib/numeric/linearEq_numsol.cpp
Index: lib/numeric/linearEq_numsol.cpp
==================================================================
--- lib/numeric/linearEq_numsol.cpp
+++ lib/numeric/linearEq_numsol.cpp
@@ -0,0 +1,46 @@
+
+//-------------------------------------------------------------
+// Linear Equation Number of Solutions. (GF(2))
+//   O(n^3)
+//
+// Verified by
+//   - SRM 590 Div1 LV2
+//
+// M[H][W] x = V[H]
+//-------------------------------------------------------------
+
+LL num_solution(int H, int W, vector<vector<int>> M, vector<int> V)
+{
+	int skipx = 0;
+	int y = 0;
+	for(int x=0; y<H && x<W; ++x)
+	{
+		if(M[y][x] == 0) {
+			bool found = false;
+			for(int yy=y+1; yy<H; ++yy)
+				if(M[yy][x] == 1) {
+					swap(M[y], M[yy]);
+					swap(V[y], V[yy]);
+					found = true;
+					break;
+				}
+			if(!found) {
+				++skipx;
+				continue;
+			}
+		}
+
+		for(int yy=y+1; yy<H; ++yy)
+			if(M[yy][x] == 1) {
+				for(int xx=x; xx<W; ++xx)
+					M[yy][xx] ^= M[y][xx];
+				V[yy] ^= V[y];
+			}
+		++y;
+	}
+
+	for(int yy=y; yy<H; ++yy)
+		if(V[yy] == 1)
+			return 0;
+	return 1LL << skipx;
+}