Segment Tree

Range Queries/SegmentTree.cpp

@@ -0,0 +1,89 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+class SegmentTree{
+
+
+	int sz;
+	vector<int> tree;
+
+public:
+
+	SegmentTree(const vector<int>& arr){
+
+		this->sz = arr.size();
+
+		tree.resize(2*this->sz+1,0);
+
+		init(arr);
+		
+	}
+
+	void init(const vector<int>& arr){
+
+		for(int i = sz-1 ; i >= 0 ; i-- )
+			tree[i+sz] = arr[i];
+
+		for(int i = sz - 1 ; i >= 1 ; i-- ){
+
+			tree[i] = tree[2*i] + tree[2*i+1];
+
+		}
+
+	}
+
+
+	void print(){
+
+		cout << "Size : " << sz << '\n';
+
+		for(int i = 0 ; i <= 2*sz ; i++ ){
+
+			cout << tree[i] << ' ';
+		}
+		cout << '\n';
+	}
+
+	int sum( int a, int b){
+
+		int s = 0;
+		a += sz , b += sz;
+
+		while( a <= b ){
+
+			if( a%2 == 1 ) s += tree[a++];
+
+			if( b%2 == 0 ) s += tree[b--];
+
+			a /= 2 , b /= 2;
+		}
+		return s;
+	}
+
+	void add(int k, int x) {
+		k += sz;
+		tree[k] += x;
+		for (k /= 2; k >= 1; k /= 2) {
+			tree[k] = tree[2*k]+tree[2*k+1];
+	}
+}
+
+
+
+};
+
+int main(){
+
+	vector<int> arr = {5,8,6,3,2,7,2,6};
+
+	SegmentTree stree(arr);
+
+
+	stree.print();
+
+	stree.add(7,1);
+	cout << "(2,7) : " << stree.sum(2,7) << '\n';
+
+	return 0;
+}