如何在树形图中找到总和？ Java的

Question

import java.util.Scanner;

public class BinaryTree {

private int info;
private BinaryTree left;
private BinaryTree right;
private int sum;

public BinaryTree()
{
    left = null;
    right = null;
}
// This is a second constructor. 
// It can tell the difference by parameter.
public BinaryTree(int theInfo)
{
    Scanner sc = new Scanner(System.in);
    int intNum;
    String s;

    info = theInfo;

    System.out.print("Does the node " + info + " have a left child (y or n)? ");
    s = sc.next();
    if (s.equals("y"))
    {
        System.out.print ("What value should go in the left child node? ");
        intNum = sc.nextInt();
        left = new BinaryTree(intNum);
    }
    System.out.print("Does the node " + info + " have a right child (y or n)? ");
    s = sc.next();
    if (s.equals("y"))
    {
        System.out.print ("What value should go in the right child node? ");
        intNum = sc.nextInt();
        right = new BinaryTree(intNum);
    }
}

public void TraverseNLR()
{

    System.out.print(info + " ");
    if (left != null)
    {
        left.TraverseNLR();
    }
    if (right != null)
    {
        right.TraverseNLR();
    }
}

public void TraverseLNR()
{
    if (left != null)
    {
        left.TraverseLNR();
    }
    System.out.print(info + " ");
    if (right != null)
    {
        right.TraverseLNR();
    }
}

public void TraverseLRN()
{

    if (left != null)
    {
        left.TraverseLRN();
    }
    if (right != null)
    {
        right.TraverseLRN();
    }
    System.out.print(info + " ");
}
/* QUESTION FUNCTION HERE */
public int sumValues()
{ 
    System.out.print(info + " ");
    sum += info;
    if (left != null)
    {
        sum += info;
        left.TraverseNLR();
    }

    if (right != null)
    {
        sum += info;
        right.TraverseNLR();
    }
    return sum;
 }
} 

---

import java.util.Scanner;

public class BinaryTester {

public static void main(String[] args) 
{
    BinaryTree myTree;
    Scanner sc = new Scanner(System.in);
    int intNum;

    System.out.print("What value should go in the root? ");
    intNum = sc.nextInt();
    myTree = new BinaryTree(intNum);
    //myTree.TraverseNLR();
    //System.out.println();
    //myTree.TraverseLNR();
    //System.out.println();
    //myTree.TraverseLRN();
    //System.out.println();
    System.out.println("Sum is " + myTree.sumValues());
    //myTree.sumValues();
  }
}

I'm having trouble finding the sum of a treemap. For example I will input:

What value should go in the root? 400
Does the node 400 have a left child (y or n)? y  
What value should go in the left child node? 100
Does the node 100 have a left child (y or n)? n
Does the node 100 have a right child (y or n)? y
What value should go in the right child node? 300
Does the node 300 have a left child (y or n)? n 
Does the node 300 have a right child (y or n)? n 
Does the node 400 have a right child (y or n)? y
What value should go in the right child node? 500
Does the node 500 have a left child (y or n)? n
Does the node 500 have a right child (y or n)? n
400 100 300 500 Sum is 1200

and get the sum is 1200 instead of the true answer 1300. There must be something that I'm not understanding recursively. How could it possibly skip the 100 from the sum? I made the sum variable globally so it would remember everything I'd assign it. Does anyone have any hints or point me in a direction of summing up an entire Treemap?

Answer 1

I don't understand what the purpose of the TraverseXXX() functions are. You should be able to just get rid of them, and rewrite your sumValues() function using recursion:

public int sumValues() {
    System.out.println(info + " ");
    int sum = info; // account for current node

    if (left != null)
        sum += left.sumValues(); // add sum of left subtree

    if (right != null)
        sum += right.sumValues(); // add sum of right subtree

    return sum;
}

Using this code for sumValues() I got the correct output of 1300:

What value should go in the root? 400
Does the node 400 have a left child (y or n)? y
What value should go in the left child node? 100
Does the node 100 have a left child (y or n)? n
Does the node 100 have a right child (y or n)? y
What value should go in the right child node? 300
Does the node 300 have a left child (y or n)? n
Does the node 300 have a right child (y or n)? n
Does the node 400 have a right child (y or n)? y
What value should go in the right child node? 500
Does the node 500 have a left child (y or n)? n
Does the node 500 have a right child (y or n)? n
400 
100 
300 
500 
Sum is 1300