113.leetcode Path Sum II(meidum)[DFS加回溯 ]

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

For 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]
]

题目要求从根到叶子节点的和等于sum的路劲集合，因此采用深度优先遍历，并将满足条件的结果保存。

class Solution {
public:
    void DFS(TreeNode* root,int sum,int current,vector<vector<int> > &result,vector<int> &mid)
    {
        if(current == sum && root == NULL)
        {
            result.push_back(mid);
            return ;
        }
        if(root != NULL)
        {
            mid.push_back(root->val);
            current += root->val;
            if(root->left == NULL && root->right == NULL)
                DFS(NULL,sum,current,result,mid);
            else
            {
                if(root->left != NULL)
                   DFS(root->left,sum,current,result,mid);
                if(root->right != NULL)
                   DFS(root->right,sum,current,result,mid);
            }
            current -= root->val;
            mid.pop_back();
        }
        return;
    }
    vector<vector<int>> pathSum(TreeNode* root, int sum) {
        vector<vector<int> > result;
        if(root == NULL) return result;
        vector<int> mid;
        int current = 0;
        DFS(root,sum,current,result,mid);
        return result;
    }
};