题解 | #重建二叉树#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param preOrder int整型一维数组 
     * @param vinOrder int整型一维数组 
     * @return TreeNode类
     */
    public TreeNode reConstructBinaryTree (int[] preOrder, int[] vinOrder) {
        // write code here
        return build(preOrder, vinOrder, 0, 0, vinOrder.length - 1);
    }

    private TreeNode build(int[] preOrder, int[] inOrder, int preStart, int inStart, int inEnd) {
        if (inEnd < inStart) {
            return null;
        }
        int rootVal = preOrder[preStart];
        TreeNode root = new TreeNode(rootVal);
        int index = 0;
        for(int i = inStart; i <= inEnd; i++) {
            if (inOrder[i] == rootVal) {
                index = i;
                break;
            }
        }
        int len = index - inStart;
        root.left = build(preOrder, inOrder, preStart + 1, inStart ,index - 1);
        root.right = build(preOrder, inOrder, preStart + len + 1, index + 1, inEnd);
        return root;
    }
}

递归地对左子树和右子树进行构建