Java实现-前序遍历和中序遍历构建二叉树

/** * Definition of TreeNode: * public class TreeNode { *     public int val; *     public TreeNode left, right; *     public TreeNode(int val) { *         this.val = val; *         this.left = this.right = null; *     } * } */  public class Solution {    /**     *@param preorder : A list of integers that preorder traversal of a tree     *@param inorder : A list of integers that inorder traversal of a tree     *@return : Root of a tree     */    public TreeNode buildTree(int[] preorder, int[] inorder) {        // write your code here        TreeNode root=null;root=preAndIn(preorder, inorder);return root;    }    private static TreeNode preAndIn(int []preorder,int []inorder){if(inorder.length==0&&preorder.length==0){return null;}int val=preorder[0];TreeNode root=new TreeNode(val);int index=0;for(int i=0;i<inorder.length;i++){if(val==inorder[i]){index=i;}}int leftInOrder[]=Arrays.copyOfRange(inorder, 0, index);int rightInOrder[]=Arrays.copyOfRange(inorder, index+1, inorder.length);int leftPreOrder[]=Arrays.copyOfRange(preorder, 1, leftInOrder.length+1);int rightPreOrder[]=Arrays.copyOfRange(preorder, index+1, preorder.length);root.left=preAndIn(leftPreOrder, leftInOrder );    root.right=preAndIn(rightPreOrder, rightInOrder);    return root;}}