Add code for fenwick tree

Author: coderick14

fenwick.cpp

@@ -0,0 +1,102 @@
+#include <bits/stdc++.h>
+#define ll long long
+using namespace std;
+
+/*
+ * POINT UPDATE, RANGE QUERY
+ */
+
+// Add delta to A[index]
+void point_update(vector<ll> &bit, ll index, ll delta) {
+    for(;index < bit.size(); index += (index & -index)) {
+        bit[index] += delta;
+    }
+}
+
+// Query sum of A[1..index]
+ll prefix_sum(vector<ll> &bit, ll index) {
+    ll sum = 0;
+    for(;index > 0; index -= (index & -index)) {
+        sum += bit[index];
+    }
+    return sum;
+}
+
+// Query sum of A[a..b]
+ll range_query(vector<ll> &bit, ll a, ll b) {
+    return prefix_sum(bit,b) - prefix_sum(bit,a-1);
+}
+
+/*
+ * RANGE UPDATE, POINT QUERY
+ */
+
+// Add delta to A[a..b]
+void range_update(vector<ll> &bit, ll a, ll b, ll delta) {
+    point_update(bit,a,delta);
+    point_update(bit,b+1,-delta);
+}
+
+// Returns A[index]
+ll point_query(vector<ll> &bit, ll index) {
+    ll sum = 0;
+    for(;index > 0; index -= (index & -index)) {
+        sum += bit[index];
+    }
+    return sum;
+}
+
+/*
+ * RANGE UPDATE, RANGE QUERY
+ */
+
+// Add delta to A[a..b]
+void range_update(vector<ll> &bit1, vector<ll> &bit2, ll a, ll b, ll delta) {
+    range_update(bit1,a,b,delta);
+    point_update(bit2,a,delta * (a-1));
+    point_update(bit2,b+1,-delta * b);
+}
+
+// Query sum of A[1..index]
+ll prefix_sum(vector<ll> &bit1, vector<ll> &bit2, ll index) {
+    return prefix_sum(bit1,index) * index - prefix_sum(bit2,index);
+}
+
+// Query sum of A[a..b]
+ll range_query(vector<ll> &bit1, vector<ll> &bit2, ll a, ll b) {
+    return prefix_sum(bit1, bit2, b) - prefix_sum(bit1, bit2, a-1);
+}
+
+
+// Slightly optimized to read a single value
+// Returns A[index]
+ll read_single_value(vector<ll> &bit, ll index) {
+    ll sum = bit[index];
+    if (index > 0) {
+        ll z = index - (index & -index);
+        index--;
+        while (index != z) {
+            sum -= bit[index];
+            index -= (index & -index);
+        }
+    }
+    return sum;
+}
+
+int main() {
+    ll i,n,q,v,l,r;
+    cin >> n;
+    vector<ll> bit(n+1,0);
+    for (i = 1; i <= n; i++) {
+        cin >> v;
+        point_update(bit,i,v);
+    }
+    cin >> q;
+    for (i = 0; i < q; i++) {
+        cin >> l >> r;
+        cout << "Sum of range [" << l << "," << r << "] = " << range_query(bit,l,r) << endl;
+        cout << "Value at " << l << " = " << read_single_value(bit,l) << endl;
+        cout << "Value at " << r << " = " << read_single_value(bit,r) << endl;
+    }
+    return 0;
+}