leetcode算法题--从中序与后序遍历序列构造二叉树

使用递归来做

class Solution {
public:
    vector in_order, post_order;
    unordered_map in_mp;
    int idx;
    TreeNode* buildTree(vector& inorder, vector& postorder) {
        in_order = inorder;
        post_order = postorder;
        int n = inorder.size();
        idx = n - 1;
        for (int i = 0; i < n; i++) {
            in_mp[inorder[i]] = i;
        }
        return getNode(0, n-1);
    }

    TreeNode* getNode(int l, int r) {
        cout << "l is" << l << "r is" << r << endl;
        if (l > r) return NULL;
        int m = in_mp[post_order[idx]];        
        TreeNode* root = new TreeNode(post_order[idx]);
        idx--;
        root->right = getNode(m+1, r);
        root->left = getNode(l, m-1);
        return root;
    }
};