LeetCode刷题（C++）——Construct Binary Tree from Preorder and Inorder Traversal（Normal）

我会带着你远行 2022-06-15 22:46 106阅读 0赞

## 题目描述 ##

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

Note:

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

/**
     * Definition for a binary tree node.
     * struct TreeNode {
     *     int val;
     *     TreeNode *left;
     *     TreeNode *right;
     *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
     * };
     */
    class Solution {
    public:
        TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
            if (preorder.size() == 0 || inorder.size() == 0 || preorder.size() != inorder.size())
    			return NULL;
    		return dfs(preorder, 0, preorder.size() - 1, inorder, 0, inorder.size() - 1);
    	}
    
    	TreeNode* dfs(vector<int>& preorder, int l1, int r1, vector<int>& inorder, int l2, int r2)
    	{
    		if (l1 > r1)
    			return NULL;
    		if (l1 == r1)
    			return new TreeNode(preorder[l1]);
    		TreeNode* root = new TreeNode(preorder[l1]);
    		for (int i = 0; i < inorder.size();i++)
    		{
    			if (inorder[i] == preorder[l1])
    			{
    				root->left = dfs(preorder, l1 + 1, l1 + i - l2, inorder, l2, i - 1);
    				root->right = dfs(preorder, l1 + i - l2 + 1, r1, inorder, i + 1, r2);
    				return root;
    			}
    		}
    		return NULL;
        }
    };