segment trees

Author: kunal-kushwaha

lectures/20-trees/code/Segment trees/Main.java

@@ -0,0 +1,9 @@
+class Main {
+  public static void main(String[] args) {
+    int[] arr = {3, 8, 6, 7, -2, -8, 4, 9};
+    SegmentTree tree = new SegmentTree(arr);
+    // tree.display();
+
+    System.out.println(tree.query(1, 6));
+  }
+}

lectures/20-trees/code/Segment trees/SegmentTree.java

@@ -0,0 +1,111 @@
+class SegmentTree {
+
+  private static class Node {
+    int data;
+    int startInterval;
+    int endInterval;
+    Node left;
+    Node right;
+
+    public Node (int startInterval, int endInterval) {
+      this.startInterval = startInterval;
+      this.endInterval = endInterval;
+    }
+  }
+
+  Node root;
+
+  public SegmentTree(int[] arr) {
+    // create a tree using this array
+    this.root = constructTree(arr, 0, arr.length - 1);
+  }
+
+  private Node constructTree(int[] arr, int start, int end) {
+    if(start == end) {
+      // leaf node
+      Node leaf = new Node(start, end);
+      leaf.data = arr[start];
+      return leaf;
+    }
+
+    // create new node with index you are at
+    Node node = new Node(start, end);
+    
+    int mid = (start + end) / 2;
+
+    node.left = this.constructTree(arr, start, mid);
+    node.right = this.constructTree(arr, mid + 1, end);
+
+    node.data = node.left.data + node.right.data;
+    return node;
+  }
+
+  public void display() {
+    display(this.root);
+  }
+  private void display(Node node) {
+    String str = "";
+
+    if(node.left != null) {
+      str = str + "Interval=[" + node.left.startInterval + "-" + node.left.endInterval + "] and data: " + node.left.data + " => "; 
+    } else {
+      str = str + "No left child";
+    }
+
+    // for current node
+    str = str + "Interval=[" + node.startInterval + "-" + node.endInterval + "] and data: " + node.data + " <= "; 
+    
+    if(node.right != null) {
+      str = str + "Interval=[" + node.right.startInterval + "-" + node.right.endInterval + "] and data: " + node.right.data; 
+    } else {
+      str = str + "No right child";
+    }
+
+    System.out.println(str + '\n');
+
+    // call recursion
+    if(node.left != null) {
+      display(node.left);
+    }
+
+    if(node.right != null) {
+      display(node.right);
+    }
+  }
+
+  // query
+  public int query(int qsi, int qei) {
+    return this.query(this.root, qsi, qei);
+  }
+  private int query(Node node, int qsi, int qei) {
+    if(node.startInterval >= qsi && node.endInterval <= qei) {
+      // node is completely lying inside query
+      return node.data;
+    } else if (node.startInterval > qei || node.endInterval < qsi) {
+      // completely outside
+      return 0;
+    } else {
+      return this.query(node.left, qsi, qei) + this.query(node.right, qsi, qei);
+    }
+  }
+
+  // update
+  public void update(int index, int value) {
+    this.root.data = update(this.root, index, value);
+  }
+  private int update(Node node, int index, int value) {
+    if (index >= node.startInterval&& index <= node.endInterval){
+      if(index == node.startInterval && index == node.endInterval) {
+        node.data = value;
+        return node.data;
+      } else {
+        int leftAns = update(node.left, index, value);
+        int rightAns = update(node.right, index, value);
+        node.data = leftAns + rightAns;
+        return node.data;
+      }
+    }
+    return node.data;
+  }
+  
+}

lectures/20-trees/code/Segment trees/pom.xml

@@ -0,0 +1,53 @@
+<project>
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>mygroupid</groupId>
+  <artifactId>myartifactid</artifactId>
+  <version>0.0-SNAPSHOT</version>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>4.12</version>
+      <type>jar</type>
+    </dependency>
+    <dependency>
+      <groupId>com.googlecode.json-simple</groupId>
+      <artifactId>json-simple</artifactId>
+      <version>1.1.1</version>
+      <type>jar</type>
+    </dependency>
+    <dependency>
+      <groupId>org.hamcrest</groupId>
+      <artifactId>hamcrest-core</artifactId>
+      <version>1.3</version>
+      <type>jar</type>
+    </dependency>
+  </dependencies>
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>de.qaware.maven</groupId>
+        <artifactId>go-offline-maven-plugin</artifactId>
+        <version>1.2.5</version>
+        <configuration>
+          <dynamicDependencies>
+            <DynamicDependency>
+              <groupId>org.apache.maven.surefire</groupId>
+              <artifactId>surefire-junit4</artifactId>
+              <version>2.20.1</version>
+              <classifier></classifier>
+              <repositoryType>PLUGIN</repositoryType>
+            </DynamicDependency>
+            <DynamicDependency>
+              <groupId>com.querydsl</groupId>
+              <artifactId>querydsl-apt</artifactId>
+              <version>4.2.1</version>
+              <classifier>jpa</classifier>
+              <repositoryType>MAIN</repositoryType>
+            </DynamicDependency>
+          </dynamicDependencies>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>

lectures/20-trees/code/Segment trees/replit.nix

@@ -0,0 +1,8 @@
+{ pkgs }: {
+    deps = [
+        pkgs.graalvm17-ce
+        pkgs.maven
+        pkgs.replitPackages.jdt-language-server
+        pkgs.replitPackages.java-debug
+    ];
+}