算法: 二叉树算法题

题目 ：给出一列格式如数据，数据格式如下所示：

{"(1,2)", "(2,4)", "(5,7)", "(7,2)", "(9,5)"}

其中，对于数组内的一个元素，与二叉树的某一节点的对应关系是： 1i是一个二叉树结果的子结果，2i是其父节点，目前有任务，要求在创建二叉树前或创建过程中对数组做校验，判断数组是否可组成一个合格的二叉树。二叉树的条件是：

• 只能有1个根节点;
• 一个子节点有且只能有 1父节点;
• 一个父节点 <=2个子节点;

核心代码（含调试过程中的一些信息）：

import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicInteger;
public class BinaryTreeIncludeSample {

        public static void main(String[] args) {
//            List listSample = Sample.getSampleList();
//            for (Sample sample : listSample) {
                System.out.println("");
                String result = start(args);
                if (result.equals("true")){
                    System.out.println("true");
                }else{
                    System.out.println("false");
                }
            //}
        }

    public static String start(String[] strArr)  {
        StringBuffer debugInfo = new StringBuffer("");
        Map parents = new ConcurrentHashMap<>();
        Map childs = new ConcurrentHashMap<>();
        if (strArr==null || strArr.length==0){
            return "";
        }
        for(String str:strArr){
            String[] ary = str.split(",");
            if (ary.length!=2){
                return "false";
            }

            if (ary[0].startsWith("(")){
                ary[0] = ary[0].substring(1);
            }
            if (ary[1].endsWith(")")){
                ary[1] = ary[1].substring(0,ary[1].length()-1);
            }

            int c = Integer.parseInt(ary[0]);
            int p = Integer.parseInt(ary[1]);


            if (!parents.containsKey(p)){
                parents.put (p,new TreeNode(p));
            }
            if (parents.get(p).left==null){
                parents.get(p).left = new TreeNode(c);
            }else if (parents.get(p).right==null){
                parents.get(p).right = new TreeNode(c);
            }else{
                // debugInfo.append(p+"有超过2个子节点").toString();
                //System.out.println(str.toString());
                return "false";
            }

            if (!childs.containsKey(c)){
                childs.put(c,new TreeNode(p,c));
            }else if (childs.get(c).left.value != c){
                //debugInfo.append(c + "有>1个父节点");
                return "false";
            }
        }


        Integer rootIndex = Arrays.asList(parents.keySet().toArray(new Integer[]{})).get(0);
        TreeNode rootNode = parents.get(rootIndex);
        parents.remove(rootIndex);
        childs.remove(rootNode.left.value);

        //构建binary tree
        AtomicInteger count = new AtomicInteger(parents.size()*4);
        createTreeNode(rootNode,rootNode,parents,childs,count);

        if (parents.size()>0) {
//            List treeNodeList = new CopyOnWriteArrayList<>();
//            inorderTraversal(rootNode,treeNodeList);
//            List treeValues =  treeNodeList.stream().map(item->{return item.value;}).collect(Collectors.toList());
//            List list = parents.keySet().stream().map(p->{return "("+parents.get(p).left.value+","+ p +")";}).collect(Collectors.toList());
//            debugInfo.append("--BinaryTree:"+treeValues.toString());
//            debugInfo.append("--异常多出节点:"+list.toString());
//            System.out.println(debugInfo.toString());
            return "false";
        }else{
            return "true";
        }
    }


    public static TreeNode createTreeNode(TreeNode rootNode, TreeNode treeNode, Map parents, Map childs, AtomicInteger count){
        if (count.get()==0){
            return rootNode;
        }
        if (rootNode!=null && childs!=null && childs.containsKey(rootNode.value)){
            TreeNode node = childs.get(rootNode.value);
            node.left = rootNode;
            rootNode = node;
            parents.remove(node.value);
            childs.remove(node.left.value);
            count.decrementAndGet();
            return createTreeNode(rootNode,treeNode,parents,childs,count);
        }

        if (treeNode!=null && treeNode.left!=null && parents!=null && parents.containsKey(treeNode.left.value)){
            treeNode.left = parents.get(treeNode.left.value);
            parents.remove(treeNode.left.value);
            count.decrementAndGet();
            return createTreeNode(rootNode,treeNode.left,parents,childs,count);
        }

        if (treeNode!=null && treeNode.right!=null && parents!=null && parents.size()>0 && parents.containsKey(treeNode.right.value)){
            treeNode.right = parents.get(treeNode.right.value);
            parents.remove(treeNode.right.value);
            count.decrementAndGet();
            return createTreeNode(rootNode,treeNode.right,parents,childs,count);
        }

        return rootNode;
    }
}

二叉树类

 public static class TreeNode{
        final private int value;
        private TreeNode left;
        private TreeNode right;


        public TreeNode(int i){
            this.value = i;
        }

        public TreeNode(int i,int leftValue){
            this.value = i;
            this.left = new TreeNode(leftValue);
        }

        public String getParentLeft(){
            return "("+ left.value +","+ value +")";
        }
    }

样本数据类

public static class Sample{
        String[] strAry;
        boolean result;
        public Sample(String[] strAry,boolean result){
            this.strAry = strAry;
            this.result = result;
        }

        public static List getSampleList(){
            List strArrList = new LinkedList(Arrays.asList(new BinaryTree.Sample[]{
                    new BinaryTree.Sample(new String[]{"(1,2)", "(2,4)", "(5,7)", "(7,2)", "(9,5)"},true),
                    new BinaryTree.Sample(new String[] {"(1,2)", "(3,2)", "(2,12)", "(5,2)"},false),
                    new BinaryTree.Sample(new String[]{"(1,2)", "(2,4)", "(5,7)", "(7,2)", "(9,5)"},true),
                    new BinaryTree.Sample(new String[]{"(1,2)", "(2,4)", "(7,2)"},true),
                    new BinaryTree.Sample(new String[]{"(1,2)", "(1,2)"},true),
                    new BinaryTree.Sample(new String[]{},true),
                    new BinaryTree.Sample(new String[]{"(1,2)", "(1,3)"},false),
                    new BinaryTree.Sample(new String[]{"(1,2)", "(2,4)", "(7,2)", "(8,8)"},false),
                    new BinaryTree.Sample(new String[]{"(1,2)", "(4,2)", "(7,2)"},false),
                    new BinaryTree.Sample(new String[]{"(1,2)", "(4,2)", "(7,9)"},false),
            }));
            return strArrList;
        }
    }

附

另外一个样本创建方法

    public static TreeNode createTree(int rootIndex, List list) {
        if (rootIndex >= list.size()) {
            return null;
        }
        TreeNode rootNode = new TreeNode(list.get(rootIndex));
        rootNode.left=createTree( 2 * rootIndex + 1, list);
        rootNode.right=createTree(2 * rootIndex + 2, list);

        return rootNode;
    }

判断二叉树是否相等

   public boolean isSamTree(TreeNode m,TreeNode n){
        if(m == null && n == null){
            return true;
        }
        if(m == null ^ n == null){
            return false;
        }
        return  (m.value == n.value && isSamTree(m.left,n.left) && isSamTree(m.right,n.right));
    }

二叉树的遍历(调试时会用上）

  /**
     * 前序遍历
     * @param root
     * @param ret
     * @return
     */
    public static List  preorderTraversal(TreeNode root, List ret){
        if(root == null)  return ret;

        if (ret==null){
           ret = new LinkedList<>();
        }
        ret.add(root);
        preorderTraversal(root.left,ret);
        preorderTraversal(root.right,ret);
        return ret;
    }


    /**
     * 中序遍历
     * @param root
     * @return
     */
    public static List inorderTraversal(TreeNode root, List list) {
        if(root == null)  return null;

        if (list==null){
            list = new LinkedList<>();
        }

        inorderTraversal(root.left,list);
        list.add(root);
        inorderTraversal(root.right,list);
        return list;
    }

    /**
     * 后序遍历
     * @param root
     * @param ret
     * @return
     */
    public static List postorderTraversal(TreeNode root, List ret) {
        if(root == null)  return ret;

        if (ret==null){
            ret = new LinkedList<>();
        }

        postorderTraversal(root.left,ret);
        ret.add(root);
        postorderTraversal(root.right,ret);
        return ret;
    }