[数据结构与算法]剑指Offer-JZ4

重建二叉树

思路

先找出根节点，然后利用递归方法构造二叉树

代码

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

public class Solution {
    public TreeNode reConstructBinaryTree(int [] pre,int [] vin) {
        if (pre == null || vin == null) {
            return null;
        }
        
        if (pre.length == 0 || vin.length == 0) {
            return null;
        }
        
        if (pre.length != vin.length) {
            return null;
        }
        
        TreeNode root = new TreeNode(pre[0]);
        
        for (int i = 0; i < vin.length; i++) {
            if (vin[i] == pre[0]) {
                root.left = reConstructBinaryTree(
                            Arrays.copyOfRange(pre, 1, i + 1),
                            Arrays.copyOfRange(vin, 0, i));
                root.right = reConstructBinaryTree(
                            Arrays.copyOfRange(pre, i + 1, pre.length),
                            Arrays.copyOfRange(vin, i + 1, vin.length));
            }
        }
        
        return root;
    }
}