Fenwick Tree snippet

Range Queries/FenwickTree.cpp

@@ -0,0 +1,83 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+
+
+class Fenwick_Tree{
+
+public:
+
+	// 1 based indexing...
+	vector<int> tree;
+	int sz;
+
+	void init(int n, const vector<int>& arr){
+		tree.resize(n+1,0);
+
+		this->sz = n;
+
+		for(int i = 1 ; i <= sz ; i++ ){
+
+			update(i, arr[i-1]);
+		}
+	}
+
+	int sum(int k){
+		int s = 0;
+
+		while(k >= 1){
+
+			s += tree[k];
+
+			k -= k & -k;
+		}
+
+		return s;
+	}
+
+	void update(int k, int val){
+
+		while( k <= sz ){
+			tree[k] += val;
+
+			k += k & -k;
+		}
+	}
+
+	void print(){
+
+		for(int i = 1 ; i <= sz ; i++ ){
+			cout << tree[i] << ' ';
+		}
+		cout << '\n';
+	}
+
+
+};
+
+
+int main(){
+
+	Fenwick_Tree fn;
+
+	vector<int> arr = {3,1,2,0,1,3,5,7,10,44,0};
+
+	fn.init( (int)arr.size(), arr);
+
+
+	fn.print();
+
+	int sum = fn.sum(10) - fn.sum(7);
+
+	cout << sum << '\n';
+
+	fn.update(10,1);
+
+	sum = fn.sum(10) - fn.sum(7);
+
+	cout << sum << '\n';
+
+
+	return 0;
+}