Update fenwick_tree.cpp

Data Structures/fenwick_tree.cpp

@@ -1,8 +1,9 @@
 template<typename T> class fenwick_tree {
-private: vector<T> FT;
+private: int N; T FT[MX];
 public:
-	fenwick_tree(int N) { FT.assign(N + 5, 0); }
-	void update(int x, T val) { if (++x) for (; x < FT.size(); x += x & -x) FT[x] += val; }
-	T query(int x) { T ret = 0; if (++x) for (; x; x -= x & -x) ret += FT[x]; return ret; }
-	T query(int x, int y) { return query(y) - query(x - 1); }
-};
+	fenwick_tree(int n) { N = n }
+	fenwick_tree(int n, T A[]) { N = n; memcpy(FT, A, sizeof FT); }
+	void update(int x, T val) { if (++x) for (; x < N; x += x&-x) FT[x] += val; }
+	T query(int x) { T ret = 0; if (++x) for (; x; x -= x&-x) ret += FT[x]; return ret; }
+	T query(int x, int y) { return query(y)-query(x-1); }
+};