implementation of Segmenet Tree from scratch

Author: NirmalSilwal

Interview Prep/section21_SegmentTrees/SegmentTree.java

@@ -0,0 +1,68 @@
+package section21_SegmentTrees;
+
+public class SegmentTree {
+
+	private class Node {
+		int data;
+		int startInterval;
+		int endInterval;
+		Node left;
+		Node right;
+	}
+
+	Node root;
+
+	public SegmentTree(int[] arr) {
+		this.root = constructTree(arr, 0, arr.length - 1);
+	}
+
+	private Node constructTree(int[] arr, int si, int ei) {
+		if (si == ei) {
+			Node baseResult = new Node(); // leaf Node
+			baseResult.data = arr[si];
+			baseResult.startInterval = si;
+			baseResult.endInterval = ei;
+
+			return baseResult;
+		}
+		Node node = new Node();
+		node.startInterval = si;
+		node.endInterval = ei;
+
+		int mid = (si + ei) / 2;
+		node.left = constructTree(arr, si, mid);
+		node.right = constructTree(arr, mid + 1, ei);
+
+		node.data = node.left.data + node.right.data;
+
+		return node;
+	}
+
+	public void display() {
+		this.display(this.root);
+	}
+
+	private void display(Node node) {
+		if (node.left == null && node.right == null) {
+			System.out.println("No left child => " + node.data + " <= No right child");
+			return;
+		}
+		String str = "";
+		if (node.left != null) {
+			str += "[" + node.left.startInterval + "-" + node.left.endInterval + "] " + node.left.data + " => ";
+		} else {
+			str = str + "No left Child";
+		}
+		str += " [" + node.startInterval + "-" + node.endInterval + "] " + node.data;
+
+		if (node.right != null) {
+			str += " <= [" + node.right.startInterval + "-" + node.right.endInterval + "] " + node.right.data;
+		} else {
+			str = str + " No right Child";
+		}
+		System.out.println(str);
+
+		display(node.left);
+		display(node.right);
+	}
+}