day47（12.28）——leetcode面试经典150

努力学算法的蒟蒻2025-12-29 12:11

106. 从中序与后序遍历序列构造二叉树

我感觉我的数据结构都要忘光光了

题目：

题解：

java 复制代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public Map<Integer,Integer> map = new HashMap<>();
    public int[] postorder;
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        for(int i=0;i<inorder.length;i++) {
            map.put(inorder[i], i);
        }
        this.postorder = postorder;
        return recur(0,inorder.length-1,0,postorder.length-1);
    }

    public TreeNode recur(int left, int right, int l,int r) {
        if(left > right || l > r) {
            return null;
        }
        int root = postorder[r];
        int i = map.get(root);

        TreeNode node = new TreeNode(root);
        node.left = recur(left, i-1, l, l+i-1-left);
        node.right = recur(i+1, right, l+i-left, r-1);
        return node;
    }
}