Algorithms/Data-structures/SegmentTreeLazy.cc at master · Deanamic/Algorithms · GitHub

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#include <bits/stdc++.h>
using namespace std;

/* Segment Tree/ Interval Tree
 * Stores information in a Heap
 * Modification, lookup in O(logn)
 * Provides Tools to update intervals
 * All intervals are [ , )
 */

struct LazySegmentTree{
	vector<int> Seg;
	vector<int> lazy;
	int n;

	void build(vector<int>& v, int m){
		n = m;
		Seg = lazy = vector<int> (4*n,0);
		build(v, 1, 0, n);
	}
	void build( vector<int>& v, int id,int left, int right){
		if(left + 1 >= right){
			Seg[id] = v[left];
			return;
		}
		int mid = (left + right)/2;
		build(v, id * 2, left, mid);
		build(v, id * 2 + 1, mid, right);
		Seg[id] = Seg[id*2] + Seg[id*2 + 1];
	}

	int find(int x, int y){
		return find(x, y, 1, 0, n);
	}
	int find(int x, int y, int id, int left, int right){
		if (lazy[id] != 0) {
			Seg[id] +=  (right-left)*lazy[id];
			if (left + 1 < right) {
				lazy[2*id] += lazy[id];             // Lazy propagation
				lazy[2*id + 1] += lazy[id];
			}
			lazy[id] = 0;
		}
		if(left >= y or right <= x){
			return 0;
		}
		if(left >= x and right <= y){
			return Seg[id];
		}
		int mid = (left + right)/2;
		return find(x, y, 2*id, left, mid) + find(x, y, 2*id + 1, mid, right);
	}

	int updateinterval(int p, int x, int y){
		updateinterval(p, 1, x, y, 0, n);
	}

	void updateinterval (int p, int id, int x, int y, int left, int right) {
		if (lazy[id] != 0) {
			Seg[id] +=  (right-left)*lazy[id];
			if (x + 1 < y) {
				lazy[2*id] += lazy[id];
				lazy[2*id + 1] += lazy[id];
			}
			lazy[id] = 0;
		}
		if(left >= y or right <= x){
			return;
		}
		if(left >= x and right <= y){
			Seg[id] +=  (right-left)*p;
			if (left + 1 < right)  {
				lazy[2*id] += p;
				lazy[2*id + 1] += p;
			}
			return;
		}
		int mid = (left + right)/2;
		updateinterval (p, 2*id, x, y, left, mid);
		updateinterval (p, 2*id + 1, x, y, mid, right);
		Seg[id] = Seg[2*id] + Seg[2*id + 1];

	}
};