Leetcode 105. Construct Binary Tree from Preorder and Inorder Traversal

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本文介绍了一种使用前序遍历和中序遍历构建二叉树的方法。通过递归算法，将前序和中序遍历序列转换为具体的二叉树结构。

Question

Given preorder and inorder traversal of a tree, construct the binary tree.

Code

  public TreeNode get(int[] preorder, int[] inorder, int i, int ileft, int iright) {
        if (ileft > iright) {
            return null;
        }
        int t = ileft;
        for (t = ileft; t <= iright && inorder[t] != preorder[i]; t++) ;
        TreeNode root = new TreeNode(preorder[i]);
        root.left = get(preorder, inorder, i + 1, ileft, t - 1);
        root.right = get(preorder, inorder, t - ileft + i + 1, t + 1, iright);
        return root;
    }

    public TreeNode buildTree(int[] preorder, int[] inorder) {

        if (preorder.length != inorder.length || preorder.length < 1) {
            return null;
        }
        return get(preorder, inorder, 0, 0, inorder.length - 1);
    }