LargestIndependentSetInTree.java

package com.interview.tree;

/**
 * http://www.geeksforgeeks.org/largest-independent-set-problem/
 */
public class LargestIndependentSetInTree {

    public int largestSet(Node root){
        if(root == null){
            return 0;
        }
        
        if(root.lis != -1){
            return root.lis;
        }
        int excl = 0;
        int left_excl = 0;
        if(root.left != null){
            left_excl = largestSet(root.left.left) + largestSet(root.left.right);
            excl += largestSet(root.left);
        }
        int right_excl = 0;
        if(root.right != null){
            right_excl = largestSet(root.right.left) + largestSet(root.right.right);
            excl += largestSet(root.right);
        }
        
        int incl = left_excl + right_excl + root.data;
        root.lis = incl;
    
        return incl > excl ? incl : excl; 
    }
    
    public static void main(String args[]){
        int inorder[] = {4,13,1,7,6,3,19};
        int preorder[] = {13,4,6,7,1,3,19};
        ConstructTreeFromInOrderPreOrder ctf = new ConstructTreeFromInOrderPreOrder();
        Node root = ctf.createTree(inorder, preorder);
        LargestIndependentSetInTree lis = new LargestIndependentSetInTree();
        System.out.println(lis.largestSet(root));
    }
}