java宽度优先将二叉树存成数组

Posted 2020-09-28 xiaoss

题目：

有一棵二叉树，请设计一个算法，按照层次打印这棵二叉树。给定二叉树的根结点root，

请返回打印结果，结果按照每一层一个数组进行储存，所有数组的顺序按照层数从上往下，且每一层的数组内元素按照从左往右排列。保证结点数小于等于500。

解题思路：

类似上一篇文章中的思路

源码：

package ss.entity;

public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    
    public int getVal() {
        return val;
    }

    public void setVal(int val) {
        this.val = val;
    }

    public TreeNode getLeft() {
        return left;
    }

    public void setLeft(TreeNode left) {
        this.left = left;
    }

    public TreeNode getRight() {
        return right;
    }

    public void setRight(TreeNode right) {
        this.right = right;
    }

    public TreeNode(int x) { val = x; }
    
    public boolean equals(Object obj) {
        return super.equals(obj);
    }
}

package ss.tree;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

import ss.entity.TreeNode;

/**
 * 有一棵二叉树，请设计一个算法，按照层次打印这棵二叉树。
 * 给定二叉树的根结点root，
 * 请返回打印结果，
 * 结果按照每一层一个数组进行储存，
 * 所有数组的顺序按照层数从上往下，
 * 且每一层的数组内元素按照从左往右排列。保证结点数小于等于500。
 * */
public class TreeDemo03 {
    public static void main(String[] args){
        TreeNode tree = new TreeNode(1);
        tree.setLeft(new TreeNode(2));
        tree.setRight(new TreeNode(3));
        
        tree.getLeft().setLeft(new TreeNode(4));
        
        tree.getRight().setLeft(new TreeNode(5));
        tree.getRight().setRight(new TreeNode(6));
        
        tree.getRight().getLeft().setLeft(new TreeNode(7));
        tree.getRight().getLeft().setRight(new TreeNode(8));
        
        int[][] a = TreeDemo03.printTree(tree);
        for(int[] b : a){
            for(int c : b){
                System.out.print(c);
            }
            System.out.println();
        }
    }
    public static int[][] printTree(TreeNode root) {
        TreeNode last = root;
        TreeNode nlast = null;
        Queue queue = new LinkedList();
        queue.add(root);
        
        List<List> list = new ArrayList<List>();
        List<Integer> temp = new ArrayList<Integer>(); 
        int maxWidth = 0; 
        while(!queue.isEmpty()){
            TreeNode tempNode = (TreeNode)queue.poll();
            temp.add(tempNode.getVal());
            if(null != tempNode.getLeft()){
                queue.add(tempNode.getLeft());
                nlast = tempNode.getLeft();
            }
            if(null != tempNode.getRight()){
                queue.add(tempNode.getRight());
                nlast = tempNode.getRight();
            }
            if(tempNode.equals(last)){
                last = nlast;
                list.add(temp);
                if(temp.size() > maxWidth)
                    maxWidth = temp.size();
                temp = new ArrayList<Integer>();
            }else{
                continue;
            }
        }
        int[][] result = new int[list.size()][maxWidth];
        for(int i = 0; i < list.size(); i++){
            List<Integer> ll = list.get(i);
            for(int j = 0; j < list.get(i).size(); j++){
                result[i][j] = ll.get(j);
            }
        }
        return result;
    }
}