NC8 二叉树根节点到叶子节点和为指定值的路径

题目描述：

给定一个二叉树和一个值\ sum sum，请找出所有的根节点到叶子节点的节点值之和等于\ sum sum 的路径，

解题分析：

采用递归的思想，依次累加，记录从根节点到叶子节点总和为sum的路径即可。

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 * };
 */

class Solution {
    
    
public:
    /**
     * 
     * @param root TreeNode类 
     * @param sum int整型 
     * @return int整型vector<vector<>>
     */
    vector<vector<int> > pathSum(TreeNode* root, int sum) {
    
    
        // write code here
        vector<vector<int>> paths;
        vector<int> path;
        recursionPathSum(root, 0, sum, path, paths);
        return paths;
    }
    
    void recursionPathSum(TreeNode* root, int currSum, int sum, vector<int> path, vector<vector<int>>& paths){
    
    
        if(root==NULL)
            return;
        path.push_back(root->val);
        currSum+=root->val;
        if(root->left == NULL && root->right==NULL && currSum==sum){
    
    
            paths.push_back(path);
            return;
        }
        recursionPathSum(root->left, currSum, sum, path, paths);
        recursionPathSum(root->right, currSum, sum, path, paths);
        return;
    }
};