Create FenwickTree.java

NASU41 · web-flow · commit b92d30c6ba92 · 2020-09-08T15:28:37.000+09:00
diff --git a/FenwickTree.java b/FenwickTree.java
@@ -0,0 +1,31 @@
+class FenwickTree{
+    private int _n;
+    private long[] data;
+
+    public FenwickTree(int n){
+        this._n = n;
+        data = new long[n];
+    }
+
+    public void add(int p, long x){
+        assert(0<=p && p<_n);
+        p++;
+        while(p<=_n){
+            data[p-1] += x;
+            p += p&-p;
+        }
+    }
+    public long sum(int l, int r){
+        assert(0<=l && l<=r && r<=_n);
+        return sum(r)-sum(l);
+    }
+
+    private long sum(int r){
+        long s = 0;
+        while(r>0){
+            s += data[r-1];
+            r -= r&-r;
+        }
+        return s;
+    }
+}
