LeetCode - 106. Construct Binary Tree from Inorder and Postorder Traversal

最新推荐文章于 2025-09-11 19:19:55 发布

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最新推荐文章于 2025-09-11 19:19:55 发布

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本文介绍了一种通过中序遍历和后序遍历构建二叉树的算法，并提供了详细的Java实现代码。该算法递归地寻找根节点，并进一步划分左右子树。

这道题目的思路与上一题基本是一样的，就不再详细写出，代码如下：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode buildTreeInPost(int preEnd, int inStart, int inEnd, int[] inorder, int[] postorder){
        if(preEnd < 0 || inStart > inEnd) return null;
        
        TreeNode root = new TreeNode(postorder[preEnd]);
        int inIndex = 0;        // index of root in postorder
        for(int i = inStart; i <= inEnd; i++){
            if(inorder[i] == root.val) inIndex = i;
        }
        root.left = buildTreeInPost(preEnd - (inEnd - inIndex) - 1, inStart, inIndex - 1, inorder, postorder);
        root.right = buildTreeInPost(preEnd - 1, inIndex + 1, inEnd, inorder, postorder);
        return root;
    }
    
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        return buildTreeInPost(postorder.length - 1, 0, inorder.length - 1, inorder, postorder);
    }
}