Added segment tree including point update and range queries(sum)

Author: prince776

DataStructures/Segment Tree/seg_tree_sum_query.cpp

@@ -0,0 +1,104 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+constexpr int MAX_SIZE = 10;
+
+int st[4 * MAX_SIZE];
+
+int combine(int x, int y)
+{
+	return x + y; // sum for sum queries
+}
+
+void buildST(int a[], int v, int l, int r)
+{
+	if (l == r)
+		st[v] = a[l];
+	else
+	{
+		int mid = (l + r) / 2;
+		buildST(a, 2 * v, l, mid);
+		buildST(a, 2 * v + 1, mid + 1, r);
+		st[v] = combine(st[v * 2], st[v * 2 + 1]);
+	} 
+}
+
+int sumQuery(int v, int nL, int nR, int l, int r)
+{
+	if (l > r)
+		return 0;
+	if (nL == l && nR == r)
+		return st[v];
+	int mid = (nL + nR) / 2;
+	return combine(
+		sumQuery(v * 2, nL, mid, l, min(r, mid)),
+		sumQuery(v * 2 + 1, mid + 1, nR, max(l, mid + 1), r)
+	);			
+}
+
+void updateST(int v, int nL, int nR, int pos, int newVal)
+{
+	if (nL == nR)
+	{
+		st[v] = newVal;
+		return;
+	}
+	int mid = (nL + nR) / 2;
+	if (pos <= mid)
+		updateST(2 * v, nL, mid, pos, newVal);
+	else
+		updateST(2 * v + 1, mid + 1, nR, pos, newVal);
+	st[v] = combine(st[2 * v], st[2 * v + 1]);
+}
+
+int32_t main()
+{
+	int a[] = {1, 2, 3, 4, 5, 6};
+	int n = sizeof(a) / sizeof(int);
+
+	buildST(a, 1, 0, n - 1);
+
+	// Test to check if seg tree works correctly.
+	random_device dev;
+	mt19937 rng(dev());
+
+    uniform_int_distribution<mt19937::result_type> dist(0,1000); // distribution in range [1, 6]
+
+    int numTests = 1000; // Test thousand times.
+    int remTest = numTests;
+    int valueUpdateCount = 0;
+    while (remTest--)
+    {
+    	int type = dist(rng) % 2;
+    	if (!type)
+    	{
+    		// Do a random update
+    		int idx = dist(rng) % n;
+    		int newVal = dist(rng);
+
+    		updateST(1, 0, n - 1, idx, newVal);
+    		a[idx] = newVal;
+    		valueUpdateCount++;
+    	}else
+    	{
+    		// Do a random range query
+    		int l = dist(rng) % n, r = dist(rng) % n;
+    		if (l > r) swap(l, r);
+
+    		int stAns = sumQuery(1, 0, n - 1, l, r);
+    		int actualAns = 0;
+    		for (int i = l; i <= r; i++)
+    			actualAns += a[i];
+
+    		if (actualAns != stAns)
+    		{
+    			cout << "Test failed\n";
+    			return 0;
+    		}
+    	}
+    }
+    cout << "Test Passed\n";
+    cout << "valueUpdateCount: " << valueUpdateCount << "\n";
+    cout << "query count: " << numTests - valueUpdateCount << "\n";
+    return 0;
+}