Create BIT2d.cc

trees/BIT2d.cc

@@ -0,0 +1,28 @@
+template<typename T>
+struct BIT2d {
+    int n, m;
+    vector<vector<T>> c;
+    BIT2d(size_t n, size_t m) : n(n), m(m), c(n + 1, vector<T>(m + 1)) {}
+    void add(size_t i, size_t j, const T& k) {
+        while (i <= n) {
+            size_t j1 = j;
+            while (j1 <= m) {
+                c[i][j1] += k;
+                j1 += lowbit(j1);
+            }
+            i += lowbit(i);
+        }
+    }
+    T getsum(size_t i, size_t j) {
+        T res = {};
+        while (i) {
+            size_t j1 = j;
+            while (j1) {
+                res += c[i][j1];
+                j1 -= lowbit(j1);
+            }
+            i -= lowbit(i);
+        }
+        return res;
+    }
+};