113.Path Sum II

class Solution {
public:
    vector<vector<int> > pathSum(TreeNode *root, int sum) {
        vector<vector<int>> res;
        vector<int> out;
        helper(root, sum, out, res);
        return res;
    }
    void helper(TreeNode* node, int sum, vector<int>& out, vector<vector<int>>& res) {
        if (!node) return;
        out.push_back(node->val);
        if (sum == node->val && !node->left && !node->right) {
            res.push_back(out);
        }
        helper(node->left, sum - node->val, out, res);
        helper(node->right, sum - node->val, out, res);
        out.pop_back();
    }
};

class Solution {
public:
    vector<vector<int> > pathSum(TreeNode *root, int sum) {
        vector<vector<int>> res;
        vector<TreeNode*> s;
        TreeNode *cur = root, *pre = NULL;
        int val = 0;
        while (cur || !s.empty()) {
            while (cur) {
                s.push_back(cur);
                val += cur->val;
                cur = cur->left;
            }
            cur = s.back(); 
            if (!cur->left && !cur->right && val == sum) {
                vector<int> v;
                for (auto it : s) {
                    v.push_back(it->val);
                }
                res.push_back(v);
            }
            if (cur->right && cur->right != pre) cur = cur->right;
            else {
                pre = cur;
                val -= cur->val;
                s.pop_back();
                cur = NULL;
            }
        }
        return res;
    }
};