如何在二叉树中打印节点数最多的关卡？

Question

class CS6085BTolani {

static Lab5BTMethods one = new Lab5BTMethods();
static int array[] ;
static int counter=0;
static int level = 0;
static int right = 0;
static int left  = 0;
static int numberOfNodesInLevel = 0;
static int levelWithMaxNodes = -1;

public static void main(String[] args) 
{
    new MyInfo().identity();
    one.createBinaryTree();
    array = new int[numberOfNodes(one.root)];
    System.out.println();
    System.out.println("Pre Order Travesal");
    one.preOrder(one.root);
    System.out.println("\n");
    System.out.println("Height of the Tree = "+one.height(one.root));
    System.out.print("\nThe Level Order of the Tree");
    one.displayTree(one.root);
    System.out.println("\n");
    System.out.println("Number of nodes in the tree : "+numberOfNodes(one.root));
    System.out.println("\nLargest Value in the tree : "+largest(one.root));
    System.out.println();
    System.out.println("Sum of Elements : " + sumOfElements(one.root));
    System.out.println();
    int x = 10;//search element
    System.out.println("Search for Number " + x +" : "+searchFor(one.root,x));
    System.out.println();
    setLargestNumberOfNodes(one.root);
    level=0;
    levelWithLargestNumberOfNodes(one.root);
    //System.out.println("Max Number of Nodes in any Level : "+(numberOfNodesInLevel+1));
    //System.out.println(levelWithMaxNodes);
}
static int numberOfNodes(Lab5BTNode root)
{
        if(root == null)
        return 0;
    else 
        return(numberOfNodes(root.right) + numberOfNodes(root.left) + 1);
}
static void toArray(Lab5BTNode root)
{

    if(root!=null)
    {
        array[counter++] = root.element;
        toArray(root.left);
        toArray(root.right);
    }
}
static int largest(Lab5BTNode root)
{
    int large = 0;
    counter=0;
    toArray(root);
    for (int i =0; i<array.length; i++) {
        if(array[i]>large){
            large = array[i];
        }
    }
    return large;
}

// program for Assignment B
static int sumOfElements(Lab5BTNode root)
{
    counter=0;
    toArray(root);
    int sum=0;
    for (int i = 0; i < array.length; i++) {
        sum = sum + array[i];
    }
    return sum;
}
static boolean searchFor(Lab5BTNode root, int n)
{
    counter=0;
    toArray(root);
    for (int i =0; i<array.length; i++)
        if(array[i]==n)
            return true;
    return false;
}
static void setLargestNumberOfNodes(Lab5BTNode root)
{
    right=0;
    left = 0;
    if (root == null) return;
    else
    {
        setLargestNumberOfNodes(root.right);
        right++;

        setLargestNumberOfNodes(root.left);
        left++;
        level++;

        if((left+right) > numberOfNodesInLevel)
        {
            numberOfNodesInLevel = left+right;

        }

    }

}
static void levelWithLargestNumberOfNodes(Lab5BTNode root)
{
 //Please Help with this code.
 //this function should print the levels with the largest number of nodes in the BT
    right=0;
    left = 0;
    if (root == null) return;
    else
    {
        levelWithLargestNumberOfNodes(root.right);
        right++;

        levelWithLargestNumberOfNodes(root.left);
        left++;
        level++;

        if((left+right) == numberOfNodesInLevel)
        {
            System.out.println("Level with largest number of Nodes: "+ (level));

        }

    }

}

}

I am trying to use the .class files provided by my professor to run a BT and I cant really print the levels with the largest number of nodes in the BT. I will put the output that i get when I run the file.

output

Pre Order Travesal
17 55 24 37 44 15 27 12 11 10 18 16 39 38 29 14 37 51 98 71 63 20 46 30 26 

Height of the Tree = 7

The Level Order of the Tree
17 
55 39 
24 37 38 29 
44 15 14 37 
27 16 51 26 
12 11 98 71 
10 18 63 30 
20 46 

Number of nodes in the tree : 25

Largest Value in the tree : 98

Sum of Elements : 848

Search for Number 10 : true

level With largest Nodes: 6
level With largest Nodes: 9
level With largest Nodes: 20
level With largest Nodes: 25

My height of the tree is 7, but the values are all wrong. Pls help. thanks.

Answer 1

I didn't test it but you should get the idea of how it could work. Basically you need to always know on which level of tree you are in your method and increase appropriate counter. I didn't use more advanced language features like maps as it looks like you only use arrays in your assignment. I also just printed the result although best practice would probably be for the method to return integer.

static void levelWithLargestNumberOfNodes(Lab5BTNode root)
{
    int height = one.height(root);
    int[] levelCounters = new int[height];
    updateCounters(root,0, levelCounters);
    int levelWithMaxNodes = findMaxIndex(levelCounters);
    System.out.println("Level with largest number of Nodes: "+ levelWithMaxNodes);
}

private static void updateCounters(Lab5BTNode root, int currentLevel, int[] levelCounters){
    if(root!=null){
        levelCounters[currentLevel]++;
        updateCounters(root.left, currentLevel+1, levelCounters);
        updateCounters(root.right, currentLevel+1, levelCounters);
    }
}

private static int findMaxIndex(int[] levelCounters) {
    int maxIndex = -1;
    int maxNodes = -1;
    for(int i = 0; i<levelCounters.length; ++i){
        if(levelCounters[i]>maxNodes){
            maxNodes = levelCounters[i];
            maxIndex = i;
        }
    }
    return maxIndex;
}

Answer 2

Used Files and PrintWriter for the solution (will work for a BT upto height 10)

static File f1;
static PrintWriter pw;

static void levelWithLargestNumberOfNodes(Lab5BTNode root) throws Exception
{

    f1 = new File("temp.txt");
    pw = new PrintWriter("temp.txt");
    boolean b1 = f1.createNewFile();
    //System.out.println(b1);
    if(!b1){
        for(int i = 0 ; i < (one.height(root)); i++)
        {
            printElementsOnALevel(one.root,i);
            pw.println();
        }
        pw.flush(); pw.close();
    }

    boolean b2 = f1.exists();
    //System.out.println(b2);

    if(b2)
    {
        Scanner sc = new Scanner(f1);
        int count = 0;
        String lev0="",lev1="",lev2="",lev3="",lev4="",lev5="",lev6="",lev7 = "",lev8 = "",lev9 = "",lev10 = "";
        while (sc.hasNextLine())
        {
            if(count==0)
                lev0 = sc.nextLine();
            if(count==1)
                lev1 = sc.nextLine();
            if(count==2)
                lev2 = sc.nextLine();
            if(count==3)
                lev3 = sc.nextLine();
            if(count==4)
                lev4 = sc.nextLine();
            if(count==5)
                lev5 = sc.nextLine();
            if(count==6)
                lev6 = sc.nextLine();
            if(count==7)
                lev7 = sc.nextLine();
            if(count==8)
                lev8 = sc.nextLine();
            if(count==9)
                lev9 = sc.nextLine();
            if(count==10)
                lev10 = sc.nextLine();
            count++;
        }
        StringTokenizer tokens = new StringTokenizer(lev0," ");
        int firstcount = tokens.countTokens();
        //System.out.println(firstcount);

        StringTokenizer tokens1 = new StringTokenizer(lev1," ");
        int secondcount = tokens1.countTokens();

        StringTokenizer tokens2 = new StringTokenizer(lev2," ");
        int thirdcount = tokens2.countTokens();

        StringTokenizer tokens3 = new StringTokenizer(lev3," ");
        int fourthcount = tokens3.countTokens();

        StringTokenizer tokens4 = new StringTokenizer(lev4," ");
        int fifthcount = tokens4.countTokens();

        StringTokenizer tokens5 = new StringTokenizer(lev5," ");
        int sixthcount = tokens5.countTokens();

        StringTokenizer tokens6 = new StringTokenizer(lev6," ");
        int seventhcount = tokens6.countTokens();

        StringTokenizer tokens7 = new StringTokenizer(lev7," ");
        int eighthcount = tokens7.countTokens();

        StringTokenizer tokens8 = new StringTokenizer(lev8," ");
        int ninthcount = tokens8.countTokens();

        StringTokenizer tokens9 = new StringTokenizer(lev9," ");
        int tenthcount = tokens9.countTokens();

        StringTokenizer tokens10 = new StringTokenizer(lev10," ");
        int eleventhcount = tokens10.countTokens();

        int temp[] = {firstcount,secondcount,thirdcount,fourthcount
            ,fifthcount,sixthcount,seventhcount,eighthcount,ninthcount,tenthcount,eleventhcount};

            int maxValue = temp[0]; 

    for(int i=1;i < temp.length;i++)
    { 
        if(temp[i] > maxValue)
        { 
            maxValue = temp[i]; 

        }
    }System.out.println("Levels with max number of Nodes i.e "+maxValue+" nodes are as follows : " );

            if(maxValue == firstcount)
                System.out.println(lev0);
            if(maxValue == secondcount)
                System.out.println(lev1);
            if(maxValue == thirdcount)
                System.out.println(lev2);
            if(maxValue == fourthcount)
                System.out.println(lev3);
            if(maxValue == fifthcount)
                System.out.println(lev4);
            if(maxValue == sixthcount)
                System.out.println(lev5);
            if(maxValue == seventhcount)
                System.out.println(lev6);
            if(maxValue == eighthcount)
                System.out.println(lev7);
            if(maxValue == ninthcount)
                System.out.println(lev8);
            if(maxValue == tenthcount)
                System.out.println(lev9);
            if(maxValue == eleventhcount)
                System.out.println(lev10);
        f1.delete();
    }

}