seg_tree_mx.cpp

/* Press F to pay respects */
#define _CRT_SECURE_NO_DEPRECATE
#pragma GCC optimize("O3")
#pragma GCC target("sse4")
#include<bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
//using namespace __gnu_pbds; 
using namespace std;
#define int long long int
#define SYNC std::ios_base::sync_with_stdio(0);cin.tie(NULL);cout.tie(NULL);
#define FRE freopen("input.txt","r",stdin);freopen("output.txt","w",stdout);
typedef long double ld;
typedef pair<int,int> ii;
typedef pair<int,ii> iii;
typedef vector<int> vi;
typedef vector<ii>   vii;
//typedef tree<int, null_type, less<int>, rb_tree_tag, 
//             tree_order_statistics_node_update> 
//    data_set;
#define rep(i,l,r)   for(int i=(l);i<(r);i++)
#define deb(x)     cout << (#x) << " is " << (x) << endl
#define dbg(x)     cout << x << ' '
#define here cout << " Hey baitch!!\n";
#define  pb push_back
#define  F  first
#define  S  second
#define all(v) (v).begin(),(v).end()
#define sz(a) (int)((a).size())
#define sq(x) ((x)*(x))
const int MOD = 1e9+7;
const int MOD1 = 998244353;
const int N = 2e5+5;
const int INF = 1000111000111000111LL;
const ld PI = 3.1415926535898;
struct seg_tree 
{

    vector<int> bit;
    vector<int> a;
    int n;
    seg_tree(int n) {
    	this-> n = n;
    	bit.assign(4*n+1,0);
    }
    seg_tree(vector<int> a) : seg_tree(a.size())
    {
    	this-> a = a;
    	build(0,0,(int)a.size()-1);
    }
	int merge(int x, int y) {
		// Function to return 
		return max(x,y);
	}
	void build(int node, int start, int end)
	{
		if(start == end)
		{
			bit[node] = a[start];
			return;
		}
		int lch = 2*node+1;		//Left Child
		int rch = 2*node+2;		//Right Child
		int mid = (start+end)/2;
		build(lch,start,mid);
		build(rch,mid+1,end);
		bit[node] = merge(bit[lch],bit[rch]);
		return;	
	}
	void update(int node, int start, int end, int pos, int val)
	{	
		if(start==end)
		{
			bit[node] = val;
			return;
		}
		int mid = (start + end)/ 2;
		int lch = 2*node + 1;
		int rch = 2*node + 2;
		if(pos<=mid)
			update(lch,start,mid,pos,val);
		else
			update(rch,mid+1,end,pos,val);
		bit[node] = merge(bit[lch],bit[rch]);
	}
	int query(int node,int start,int end, int l, int r)
	{
		if(l>end or r<start or start>end)
			return -INF;
		if(l<=start and r>=end)
			return bit[node];
		int lch = 2*node+1;		//Left Child
		int rch = 2*node+2;		//Right Child
		int mid = (start+end)/2;
		return merge(query(lch,start,mid,l,r),query(rch,mid+1,end,l,r));
	}
};