Code For Merge_Sort_Tree added

data_structures/trees/MergeSortTree.cpp

@@ -0,0 +1,104 @@
+// C++ program to count number of smaller or 
+// equal to given number and given row range. 
+#include<bits/stdc++.h> 
+using namespace std; 
+
+const int MAX = 1000; 
+
+// Constructs a segment tree and stores sTree[] 
+void buildTree(int idx, int ss, int se, vector<int> a[], 
+								vector<int> sTree[]) 
+{ 
+	/*leaf node*/
+	if (ss == se) 
+	{ 
+		sTree[idx] = a[ss]; 
+		return; 
+	} 
+
+	int mid = (ss+se)/2; 
+
+	/* building left subtree */
+	buildTree(2*idx+1, ss, mid, a, sTree); 
+
+	/* building right subtree */
+	buildTree(2*idx+2, mid+1, se, a, sTree); 
+
+	/* merging left and right child in sorted order */
+	merge(sTree[2*idx+1].begin(), sTree[2*idx+1].end(), 
+		sTree[2*idx+2].begin(), sTree[2*idx+2].end(), 
+		back_inserter(sTree[idx])); 
+} 
+
+// Recursive function to count smaller elements from row 
+// a[ss] to a[se] and value smaller than or equal to k. 
+int queryRec(int node, int start, int end, int ss, int se, 
+		int k, vector<int> a[], vector<int> sTree[]) 
+{ 
+	/* If out of range return 0 */
+	if (ss > end || start > se) 
+		return 0; 
+
+	/* if inside the range return count */
+	if (ss <= start && se >= end) 
+	{ 
+		/* binary search over the sorted vector 
+		to return count >= X */
+		return upper_bound(sTree[node].begin(), 
+						sTree[node].end(), k) - 
+						sTree[node].begin(); 
+	} 
+
+	int mid = (start+end)/2; 
+
+	/*searching in left subtree*/
+	int p1 = queryRec(2*node+1, start, mid, ss, se, k, a, sTree); 
+
+	/*searching in right subtree*/
+	int p2 = queryRec(2*node+2, mid+1, end, ss, se, k, a, sTree); 
+
+	/*adding both the result*/
+	return p1 + p2; 
+} 
+
+// A wrapper over query(). 
+int query(int start, int end, int k, vector<int> a[], int n, 
+								vector<int> sTree[]) 
+{ 
+return queryRec(0, 0, n-1, start, end, k, a, sTree); 
+} 
+
+// Driver code 
+int main() 
+{ 
+	int n = 3; 
+	int arr[][3] = { {2, 4, 5}, 
+					{3, 4, 9}, 
+					{6, 8, 10}}; 
+
+	// build an array of vectos from above input 
+	vector<int> a[n]; 
+	for (int i=0; i<n; i++) 
+		for (int j=0; j<n; j++) 
+			a[i].push_back(arr[i][j]); 
+
+	// Construct segment tree 
+	vector<int> sTree[MAX]; 
+	buildTree(0, 0, n-1, a, sTree); 
+
+	/* un-comment to print merge sort tree*/
+	/*for (int i=0;i<2*n-1;i++) 
+	{ 
+		cout << i << " "; 
+		for (int j=0;j<sTree[i].size();j++) 
+		cout << sTree[i][j]<<" "; 
+		cout << endl; 
+	}*/
+
+	// Answer queries 
+	cout << query(0, 1, 5, a, n, sTree) << endl; 
+	cout << query(1, 2, 1, a, n, sTree) << endl; 
+	cout << query(0, 2, 6, a, n, sTree) << endl; 
+
+	return 0; 
+}