LeetCode之Construct Binary Tree from Inorder and Postorder Traversal

 /*此题利用二叉树中序和后序遍历的性质，递归重建二叉树。*/
class Solution {
public:
    TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
        if(inorder.empty() || inorder.size() != postorder.size()) return nullptr;
        return buildTree(inorder, 0, inorder.size()-1, postorder, 0, postorder.size()-1);
    }
    
    TreeNode* buildTree(const vector<int> &inorder, int in_left, int in_right,
    const vector<int> &postorder, int post_left, int post_right){
        if(in_left > in_right) return nullptr;
        TreeNode *root = new TreeNode(postorder[post_right]);
        int mid(in_left);
        while(mid <= in_right && inorder[mid] != postorder[post_right]) ++mid;
        int left_length = mid - in_left;
        root->left = buildTree(inorder, in_left, mid-1,
        postorder, post_left, post_left+left_length-1);
        root->right = buildTree(inorder, mid+1, in_right,
        postorder, post_left+left_length, post_right-1);
        return root;
    }
};