【Leetcode】113. Path Sum II 路径总和 II

113. Path Sum II
     Given a binary tree and a sum, find all root-to-leaf paths where each path’s sum equals the given sum.
     Note: A leaf is a node with no children.
     Example:
     Given the below binary tree and sum = 22,

      5
     / \
    4   8
   /   / \
  11  13  4
 /  \    / \
7    2  5   1

Return:

[
[5,4,11,2],
[5,8,4,5]
]
【大意】给定一个二叉树和一个目标和，找到所有从根节点到叶子节点路 径总和等于给定目标和的路径
【思路】DFS遍历，从跟到叶子一条一条的递归。

class Solution {
public:
    vector<vector<int>> pathSum(TreeNode* root, int sum) {
          vector<vector<int>> vvi;
          vector < int > vi;    
          paths(root, sum,vvi,vi);
          return vvi;
             
    }
    
void paths(TreeNode* root, int sum,vector < vector < int > >  &vvi,vector < int > &vi)
    {       
        if(root == NULL) 
            return ;
         if( root->val == sum && root->left == NULL && root->right == NULL )    
           {
                vi.push_back(root->val);
                vvi.push_back(vi);
                vi.pop_back();
                return ;
            }
           vi.push_back(root->val);
           paths(root->left,sum-root->val,vvi,vi);
           paths(root->right,sum-root->val,vvi,vi); 
          vi.pop_back();
    }
    
};