Merge pull request #3252 from isheoran/subhash-RMQ-Segment-Tree

Added C++ Implementation of Range Maximum Query using Segment Tree

data_structures/SegmentTree/Range_Maximum_Query/c++/Range_Maximum_Query_Segment_Tree.cpp

@@ -0,0 +1,110 @@
+
+/*
+
+C++ Implementation of Segment Tree for range maximum query with updates.
+Initially you will be given an array and then you will be given queries of two types :-
+ 1) l r (In this query you have to find maximum value over range l to r in array)
+ 2) pos val (In this type of query you have to update the value of array at position pos to val)
+
+
+TestCases
+Input :-
+
+5 2
+1 20 4 6 20
+2 1 -4
+1 1 3
+
+Output :-
+6
+
+*/
+
+#include <bits/stdc++.h>
+using namespace std;
+
+//Class implementation of Segment Tree
+class SegmentTree{
+    vector<int>tree;
+    const int inf = 1e9;
+    int n;
+public:
+    SegmentTree(){}
+
+    SegmentTree(vector<int>a) {
+        this->n = a.size();
+        tree.resize(4*n);
+        build(a,0,n-1,1);
+    }
+
+    //Build function to build tree over given array a
+    void build(vector<int>&a,int st,int en,int node) {
+        if(st == en) {
+            tree[node] = a[st];
+            return;
+        }
+        int mid = (st+en)/2;
+        build(a,st,mid,2*node);
+        build(a,mid+1,en,2*node+1);
+        tree[node] = max(tree[2*node],tree[2*node+1]);
+    }
+
+    //Update function to update the tree while update the value of array at index pos to val
+    void update(int pos,int val,int st,int en,int node) {
+        if(st > pos or en < pos) return;
+        if(st == en) {
+            tree[node] = val;
+            return;
+        } 
+        int mid = (st+en)/2;
+        update(pos,val,st,mid,2*node);
+        update(pos,val,mid+1,en,2*node+1);
+        tree[node] = max(tree[2*node],tree[2*node+1]);
+    }
+
+    int query(int l,int r,int st,int en,int node) {
+        if(st > r or en < l) return -inf;
+        if(st >= l and en <= r) return tree[node];
+        int mid = (st+en)/2;
+        return max(query(l,r,st,mid,2*node),query(l,r,mid+1,en,2*node+1));
+    }
+};
+
+signed main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);cout.tie(nullptr);
+
+    int n,q;
+    //n is number of elements in array
+    //q is the number of queries
+
+    cin>>n>>q;
+
+    vector<int>a(n);
+    //Input the array a
+    for(int i=0;i<n;i++) {
+        cin>>a[i];
+    }
+
+    SegmentTree tr(a);
+
+    while(q--) {
+        int t;
+        //t is type of query
+        cin>>t;
+        if(t == 1) {
+            int l,r;
+            //l, r is the range of the query to find maximum over array
+            cin>>l>>r;
+            cout<<tr.query(l,r,0,n-1,1)<<"\n";
+        }
+        else {
+            int pos,val;
+            cin>>pos>>val;
+            //Update a[pos] = val;
+            tr.update(pos,val,0,n-1,1);
+        }
+    }
+
+    return 0;
+}