重建二叉树

package leetcode.剑指Offer.重建二叉树;

import java.util.Arrays;

public class LeetCode {
    public static void main(String[] args) {
        System.out.println(new Solution().buildTree(new int[] {3, 9, 20, 15, 7}, new int[] {9, 3, 15, 20, 7}));
    }
}

class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        if (preorder == null || inorder == null || preorder.length == 0 || preorder.length != inorder.length) {
            return null;
        }

        TreeNode rootTreeNode = new TreeNode(preorder[0]);

        if (preorder.length == 1) {
            return rootTreeNode;
        }

        int rootValue = preorder[0];
        int rootIndex = 0;

        for (int i = 0; i < inorder.length; i++) {
            if (inorder[i] == rootValue) {
                rootIndex = i;
                break;
            }
        }

        rootTreeNode.left = buildTree(Arrays.copyOfRange(preorder, 1, rootIndex + 1), Arrays.copyOfRange(inorder, 0, rootIndex));
        rootTreeNode.right = buildTree(Arrays.copyOfRange(preorder, rootIndex + 1, preorder.length), Arrays.copyOfRange(inorder, rootIndex + 1, inorder.length));
        return rootTreeNode;
    }
}

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

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

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