LeetCode Construct Binary Tree from Inorder and Postorder Traversal

最新推荐文章于 2022-01-01 11:35:53 发布

coobj2008

最新推荐文章于 2022-01-01 11:35:53 发布

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本文详细介绍了如何通过中序和后序遍历序列构建一棵二叉树，包括创建树节点的方法及递归实现过程。

题目：

Given inorder and postorder traversal of a tree, construct the binary tree.

Note:
You may assume that duplicates do not exist in the tree.

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
        TreeNode *root = createTree(inorder, 0, inorder.size()-1, postorder, 0, postorder.size()-1);
        return root;
    }
    TreeNode *createTree(vector<int> &inorder, int inBeg, int inEnd, vector<int> &postorder, int postBeg, int postEnd) {
        if(postBeg > postEnd)
            return NULL;
        int rootVal = postorder[postEnd];
        int index;
        for(int i = inBeg; i <= inEnd; i++) {
            if(inorder[i] == rootVal) {
                index = i;
                break;
            }
        }
        int len = index-inBeg;
        TreeNode *root = new TreeNode(rootVal);
        root->left = createTree(inorder, inBeg, index-1, postorder, postBeg, postBeg+len-1);
        root->right = createTree(inorder, index+1, inEnd, postorder, postBeg+len, postEnd-1);
        return root;
    }
};