Given a binary tree, collect a tree's nodes as if you were doing this: Collect and remove all leaves, repeat until the tree is empty.

Example:
Given binary tree

          1

         / \

        2   3

       / \

      4   5

Returns [4, 5, 3], [2], [1].

Explanation:

1. Removing the leaves [4, 5, 3] would result in this tree:

          1

         /

        2

2. Now removing the leaf [2] would result in this tree:

          1

3. Now removing the leaf [1] would result in the empty tree:

          []

Returns [4, 5, 3], [2], [1].

 vector<vector<int>> findLeaves(TreeNode* root) {

        vector<vector<int>> ret;

        removeLeaves(ret, root);

        return ret;

    }

    int removeLeaves(vector<vector<int>> & ret, TreeNode* root) {

        if (root == NULL) return ;

        int d1 = removeLeaves(ret, root->left);

        int d2 = removeLeaves(ret, root->right);

        int lev = max(d1, d2) + ;

        if (ret.size() <= lev) ret.resize(lev);

        ret[lev - ].push_back(root->val);

        return lev;

    }