剑指offer. 面试题34. 二叉树中和为某一值的路径. 二叉树练习

输入一棵二叉树和一个整数，打印出二叉树中节点值的和为输入整数的所有路径。从树的根节点开始往下一直到叶节点所经过的节点形成一条路径。

 

    void recursion(TreeNode *root, vector<vector<int>> &out, vector<int> &rows, int preSum, int sum) {

        if(nullptr == root)
            return;

        if(preSum + root->val == sum && nullptr == root->left && nullptr == root->right) {

            rows.push_back(root->val);
            out.push_back(rows);
            rows.erase(rows.end() - 1);
            return;
        }

        rows.push_back(root->val);
        recursion(root->left, out, rows, preSum + root->val, sum);
        recursion(root->right, out, rows, preSum + root->val, sum);
        rows.erase(rows.end() - 1);
    }

    vector<vector<int>> pathSum(TreeNode* root, int sum) {

        vector<int> rows;
        vector<vector<int>> out;
        recursion(root, out, rows, 0, sum);
        return out;
    }