leetcode.106 中序后序构造二叉树

class Solution {
public:
    TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
        if(inorder.size() == 0 || postorder.size() == 0) return NULL;
        return traversal(inorder, postorder);
    }

    TreeNode* traversal(vector<int>& inorder, vector<int>& postorder) {
        if(postorder.size() == 0) return NULL;
        
        int rootValue = postorder[postorder.size() - 1];
        TreeNode* root = new TreeNode(rootValue);

        if(postorder.size() == 1) return root;

        int delimiterIndex;
        for(delimiterIndex = 0; delimiterIndex < inorder.size(); delimiterIndex++) {
            if(inorder[delimiterIndex] == rootValue) break;
        }

        vector<int> leftInorder(inorder.begin(), inorder.begin() + delimiterIndex);
        vector<int> rightInorder(inorder.begin() + delimiterIndex + 1, inorder.end());

        postorder.resize(postorder.size() - 1);

        vector<int> leftPostorder(postorder.begin(), postorder.begin() + leftInorder.size());
        vector<int> rightPostorder(postorder.begin() + leftInorder.size(), postorder.end());

        root->left = traversal(leftInorder, leftPostorder);
        root->right = traversal(rightInorder, rightPostorder);
        return root;
    }
};