重建二叉树

递归建立二叉树。

public class Solution {
    class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode(int x) {
            val = x;
        }
    }

    private TreeNode create(int[] pre, int[] in, int _i, int _j, int i, int j){
        if (i > j || i < 0) return null;
        if (j-i == 0) {
            return new TreeNode(pre[_i]);
        }
        int k = 0;
        while (in[k] != pre[_i]) ++k;
        TreeNode treeNode = new TreeNode(pre[_i]);
        treeNode.left = create(pre, in, _i+1, _i+(k-i), i, k-1);
        treeNode.right = create(pre, in, _i+(k-i)+1, _j, k+1, j);

        return treeNode;
    }

    public TreeNode reConstructBinaryTree(int[] pre, int[] in) {
        return create(pre,  in,0, pre.length-1, 0, in.length-1);
    }
}