根據前序遍歷和中序遍歷重建二叉樹

     /**
     * Definition for binary tree
     */
    public class TreeNode {
          int val;
          TreeNode left;
          TreeNode right;
          TreeNode(int x) { val = x; }
     }

    public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        //創建新節點
        TreeNode node = new TreeNode(0);
        //判斷是否爲空
        if (pre.length == 0  || in.length == 0){
            return null;
        }else {
            node.val = pre[0];
        }
        int[] p_left,p_right,left_num,right_num;

            for (int j = 0; j < in.length; j++) {
                     if (pre[0] == in[j]){
                         //獲取前序遍歷左子樹 p_left = Arrays.copyOfRange(pre,0,j); 數組複製範圍
                         p_left = new int[j];
                         for (int k = 0; k < j; k++) {
                             p_left[k] = pre[k+1];
                         }
                         //獲取前序遍歷右子樹
                         p_right = new int[pre.length -j-1];
                         for (int k = 0; k < pre.length -j-1; k++) {
                             p_right[k] = pre[k+j+1];
                         }
                         //獲取中序遍歷左子樹
                         left_num = new int[j];
                         for (int k = 0; k < j; k++) {
                             left_num[k] = in[k];
                         }
                         //獲取中序遍歷右子樹
                         right_num = new int[in.length-j-1];
                         for (int k = 0; k < in.length-j-1; k++) {
                             right_num[k] = in[k+j+1];
                         }

                         node.left = reConstructBinaryTree(p_left,left_num);
                         node.right = reConstructBinaryTree(p_right,right_num);
                     }
            }

            return node;
        }