输入先序和中序构造二叉树

最新推荐文章于 2022-10-18 14:52:44 发布

原创最新推荐文章于 2022-10-18 14:52:44 发布 · 892 阅读

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#二叉树

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本文介绍了一种通过前序遍历和中序遍历数组重构二叉树的方法，并提供了详细的Java实现代码。通过递归的方式创建节点，实现了左右子树的构建。

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public static TreeNode reConstructTreeNode(int[] pre,int[] in)
    {
        //获取节点的根
        int rootVal = pre[0];
        //定义一个节点,将根节点值赋值给构造的节点
        TreeNode treeNode = new TreeNode(rootVal);
        //获取根的左子树的中序
        ArrayList<Integer> li = new ArrayList<Integer>();
        int rootPos = 0;
        for (int i = 0; rootVal != in[i] ; i++) {
            rootPos ++;
            li.add(in[i]);
        }
        //获取根的右子树的中序
        ArrayList<Integer> ri = new ArrayList<Integer>();
        for (int i = rootPos + 1; i < in.length; i++) {
            ri.add(in[i]);
        }
        //获取根的左子树的先序
        ArrayList<Integer> lp = new ArrayList<Integer>();
        for (int i = 1; i < rootPos + 1; i++) {
            lp.add(pre[i]);
        }
        //获得根的右子树的先序
        ArrayList<Integer> rp = new ArrayList<Integer>();
        for (int i = rootPos + 1; i < pre.length; i++) {
            rp.add(pre[i]);
        }
        if(lp.size() == 0 || li.size() == 0)
        {
            treeNode.leftTree = null;
        }
        else if(rp.size() == 0 || rp.size() == 0)
        {
            treeNode.rightTree = null;
        }
        //若左右子树都不为空
        if(lp.size() != 0)
        {
            //左先序赋值给数组
            int[] lpArr = new int[lp.size()];
            for (int i = 0; i < lpArr.length; i++) {
                lpArr[i] = lp.get(i);
            }
            //左中序赋值给数组
            int[] liArr = new int[li.size()];
            for (int i = 0; i < liArr.length; i++) {
                liArr[i] = li.get(i);
            }
            //右先序赋值给数组
            int[] rpArr = new int[rp.size()];
            for (int i = 0; i < rpArr.length; i++) {
                rpArr[i] = rp.get(i);
            }
            //右先序赋值给数组
            int[] riArr = new int[ri.size()];
            for (int i = 0; i < riArr.length; i++) {
                riArr[i] = ri.get(i);
            }
            treeNode.leftTree = reConstructTreeNode(lpArr, liArr);
        }
        if(rp.size() != 0)
        {
            //左先序赋值给数组
            int[] lpArr = new int[lp.size()];
            for (int i = 0; i < lpArr.length; i++) {
                lpArr[i] = lp.get(i);
            }
            //左中序赋值给数组
            int[] liArr = new int[li.size()];
            for (int i = 0; i < liArr.length; i++) {
                liArr[i] = li.get(i);
            }
            //右先序赋值给数组
            int[] rpArr = new int[rp.size()];
            for (int i = 0; i < rpArr.length; i++) {
                rpArr[i] = rp.get(i);
            }
            //右先序赋值给数组
            int[] riArr = new int[ri.size()];
            for (int i = 0; i < riArr.length; i++) {
                riArr[i] = ri.get(i);
            }
            treeNode.rightTree = reConstructTreeNode(rpArr, riArr);
        }
        return treeNode;


    }

节点的类：


class TreeNode
{
    int Val;
    TreeNode leftTree;
    TreeNode rightTree;
    TreeNode(int Val)
    {
        this.Val = Val;
    }
    }