chore(CPlusPlus): add iterative segment tree (#521)

algorithms/CPlusPlus/README.md

@@ -117,7 +117,7 @@
 10. [Finding the height of a given tree](Trees/Height-Of-Tree.cpp)
 11. [Finding the elements of a tree visible from top view](Trees/Top-View-Of-A-Tree.cpp)
 12. [Binary Tree Implementation](Trees/binary-tree-implementation.cpp)
-
+13. [Iterative Segment Tree](Trees/IterativeSegmentTree.cpp)
 # Maths
 
 1. [Kaprekar Number](Maths/Kaprekar-number.cpp)

algorithms/CPlusPlus/Trees/IterativeSegmentTree.cpp

@@ -0,0 +1,91 @@
+//Find the Maximum in given range with updates.
+#include <bits/stdc++.h>
+using namespace std;
+//struct s(n,x);
+struct SegTree
+{
+    typedef int T;
+    static constexpr T unit = -1e9;
+    T f(T a, T b) { return max(a, b); } // (any associative fn)
+    vector<T> s;
+    int n;
+    SegTree(int _n = 0, T def = unit) : s(2 * _n, def), n(_n) {}
+    //O(logn)
+    void update(int pos, T val)
+    {
+        for (s[pos += n] = val; pos /= 2;)
+            s[pos] = f(s[pos * 2], s[pos * 2 + 1]);
+    }
+    //O(logn)
+    T query(int b, int e)
+    { // query [b, e)
+        T ra = unit, rb = unit;
+        for (b += n, e += n; b < e; b /= 2, e /= 2)
+        {
+            if (b % 2)
+                ra = f(ra, s[b++]);
+            if (e % 2)
+                rb = f(s[--e], rb);
+        }
+        return f(ra, rb);
+    }
+};
+int main()
+{
+    int n;
+    cin >> n;
+    vector<int> v(n);
+
+    for (int i = 0; i < n; i++)
+    {
+        cin >> v[i];
+    }
+    SegTree s(n + 1);
+    //Building of Segment Tree in O(n*(log(n)))
+    for (int i = 0; i < n; i++)
+    {
+        s.update(i + 1, v[i]);
+    }
+    //queries
+
+    int q;
+    cin >> q;
+    while (q--)
+    {
+        int t;
+        //two types of queries
+        //1) t = 1 change element at index i to u
+        //2) t = 2 print the sum of elements in range [l,r]
+        cin >> t;
+        if (t == 1)
+        {
+            int id, u;
+            cin >> id >> u;
+            id--;                //changing to zero base
+            s.update(id + 1, u); //updating the delta
+        }
+        else
+        {
+            int l, r;
+            cin >> l >> r;
+            cout << s.query(l, r + 1) << endl;
+        }
+    }
+}
+
+// Time Complexity:
+// O(nlogn)
+// Space Complexity:
+// O(n)
+
+// Test Cases:
+// Input:
+// 5
+// 1 3 4 7 -15
+// 3
+// 2 2 5
+// 1 3 15
+// 2 2 5
+// Output:
+// 7
+// 15