题解 | #重建二叉树#

/**
 * 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* reConstructBinaryTree(vector<int> pre,vector<int> vin) {
        // base case
        if (pre.empty() || vin.empty()) return nullptr;
	  
        // recursively build tree
        // root node
        TreeNode* root = new TreeNode(pre[0]);
        // middle index in vin
        int midi = find(vin.begin(), vin.end(), pre[0]) - vin.begin();
        // left tree
        vector<int> preleft(pre.begin()+1, pre.begin()+1+midi);
        vector<int> vinleft(vin.begin(), vin.begin()+midi);
        TreeNode* lefttree = reConstructBinaryTree(preleft, vinleft);
        // right tree
        vector<int> preright(pre.begin()+1+midi, pre.end());
        vector<int> vinright(vin.begin()+1+midi, vin.end());
        TreeNode* righttree = reConstructBinaryTree(preright, vinright);
        // construct the tree
        root->left = lefttree;
        root->right = righttree;

        return root;
    }
};

如何从一个 vector vec 中取一个 sub vector subvec，下标从n到m：

vector<int> subvec(vec.begin()+n, vec.begin()+m);

取整个 vector：

vector<int> subvec(vec.begin(), vec.end());