Segment Tree data structure in C++. (#253)

Segment Tree data structure in C++.

Author: piyush6348

segment_tree.cpp

@@ -0,0 +1,96 @@
+#include<bits/stdc++.h>
+using namespace std;
+//Sum of a given segment;
+int getSumUtil(int *st, int ss, int se, int qs, int qe, int si)
+{
+	//starting query is less than starting index of the seg and ending query is greater than 
+	//ending index of the segment, then return the value store at that index;
+	if(qs <= ss && qe >= se)
+		return st[si];
+	if(qs > se || qe < ss)
+		return 0;
+	int mid = (ss + se) / 2;
+	return getSumUtil(st, ss, mid, qs, qe, 2*si+1) + getSumUtil(st, mid+1, se, qs, qe, 2*si+2);
+}
+void updateValueUtil(int *st, int ss, int se, int i, int diff, int si)
+{
+	if(i < ss || i > se)
+		return;
+	st[si] = st[si] + diff;
+	if(ss != se)
+	{
+		int mid = (ss + se) / 2;
+		//Break the segment tree into two parts and compute for each part to get updated segment tree;
+		updateValueUtil(st, ss, mid, i, diff, 2*si+1);
+		updateValueUtil(st, mid+1, se, i, diff, 2*si+2);
+	}
+}
+//Update the value at a particular index in the array;
+void updateValue(int arr[], int *st, int n, int i, int val)
+{
+	int diff = val - arr[i];
+	arr[i] = val;
+	updateValueUtil(st, 0, n-1, i, diff, 0);
+}
+//Calculate sum of a given segment in the array;
+int getSum(int* st, int n, int qs, int qe)
+{
+	//If starting query is less than 0 or ending query is greater than length of the array
+	//or starting query is greater than ending query the program will be terminated;
+	if(qs < 0 || qe > n-1 || qe < qs)
+		return -1;
+	return getSumUtil(st, 0, n-1, qs, qe, 0);
+}
+//Computer power in log(n) time complexity;
+int pown(int a, int b)
+{
+	if(b == 0)
+		return 1;
+	if(b == 1)
+		return a;
+	return pown(a, b/2) * pown(a, b - b/2);
+}
+int constructSTUtil(int arr[], int ss, int se, int *st, int si)
+{
+	//if function goes to leaf node then data value will be value store in that segment in the given array;
+	if(ss == se)
+	{
+		st[si] = arr[se];
+		return arr[ss];
+	}
+	int mid = (ss + se) / 2;
+	//Data value store in a node is the sum of data value store it's two child;
+	st[si] = constructSTUtil(arr, ss, mid, st, 2*si+1) + constructSTUtil(arr, mid+1, se, st, 2*si+2);
+	return st[si];
+}
+//Construct the segment tree;
+int *constructST(int arr[], int n)
+{
+	int x = (int)(ceil(log2(n)));
+	//Total no of leaf node in the segment tree;
+	int max_size = 2 * pown(2, x) - 1;
+	int *st = new int[max_size];
+	//Construct the segment tree where data value store in a node is the sum of data value store it's two child;
+	int val = constructSTUtil(arr, 0, n-1, st, 0);
+	for(int i = 0; i < max_size; i++)
+		cout << st[i] << " ";
+	cout << endl;
+	return st;
+}
+int main()
+{
+	int n;
+	cin>>n;
+	int arr[n+5];
+	for(int i = 0; i < n; i++)
+		cin>>arr[i];
+	//Construct the Segment Tree;
+	int *st = constructST(arr,n);
+	//Get the sum of a given range;
+	cout << getSum(st, n, 1, 3) << endl;
+	//Update the value of a particular index in the given array;
+	updateValue(arr, st, n, 1, 10);
+	//Get the sum of a given range;
+	cout << getSum(st, n, 1, 3) << endl;
+	return 0;
+}