Update SegmentTree.md

Author: amirhamza05

Tutorial/SegmentTree.md

@@ -3,5 +3,79 @@
 ### KGSS - Maximum Sum
 - **Link:** https://www.spoj.com/problems/KGSS/
 - **Algorithm:** Segment tree, Pair Segment Tree
- 
+
 > Firstly store all value
+<details>
+  <summary>Code</summary>
+  
+  ```c++
+#include<bits/stdc++.h>
+#define MAX 100007
+using namespace std;
+typedef long long ll;
+
+pair<int,int>tree[4*MAX];
+int in[MAX];
+
+pair<int,int>cmp(pair<int,int>a,pair<int,int>b) {
+    vector<int>v;
+    v.push_back(a.first);
+    v.push_back(a.second);
+    v.push_back(b.first);
+    v.push_back(b.second);
+    sort(v.begin(),v.end(),greater<int>());
+    return {v[0],v[1]};
+}
+
+void build(int node,int l,int r) {
+    if(l == r) {
+        tree[node] = {in[l],-1};
+        return;
+    }
+    int mid = (l+r)/2;
+    build(node*2,l,mid);
+    build(node*2+1,mid+1,r);
+    tree[node] = cmp(tree[node*2],tree[node*2+1]);
+}
+
+void update(int node,int l,int r,int i,int val) {
+    if(l>i || r<i)return;
+    if(l == r && l == i) {
+        tree[node] = {val,-1};
+        return;
+    }
+    int mid = (l+r)/2;
+    update(node*2,l,mid,i,val);
+    update(node*2+1,mid+1,r,i,val);
+    tree[node] = cmp(tree[node*2],tree[node*2+1]);
+}
+
+pair<int,int>query(int node,int l,int r,int i,int j) {
+    if(l>j || r<i)return {-1,-1};
+    if(l >= i && r <=j)return tree[node];
+    int mid = (l+r)/2;
+    return cmp(query(node>>1,l,mid,i,j),query(node>>1|1,mid+1,r,i,j));
+}
+
+int main() {
+    int test=4,t,i,n,q,l,r;
+    char type;
+    cin >> n;
+    for(i=1; i<=n; i++)cin >> in[i];
+    build(1,1,n);
+    cin >> q;
+    for(i=0; i<q; i++) {
+        cin >> type >> l >> r;
+        if(type == 'Q') {
+            pair<int,int>get = query(1,1,n,l,r);
+            cout << (get.first+get.second) << "\n";
+        } else update(1,1,n,l,r);
+    }
+
+    return 0;
+}
+
+```
+</details> 
+
+