[leetcode]Path Sum II

Posted 2020-06-27 lxydo

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]
]

分析：
这道题目算是Path Sum的延伸，只不过要求出所有从根到树叶的路径上节点和为给定值的路径，并放到一个vector中返回。采取类似于Path Sum递归思路，每次递归都会建立一个新的vector，复制之前的vector内容，并将当前节点的值放入，如果当前节点是叶节点，并且路径上节点和满足要求，就将新的vector放入最终返回的vector中。
代码：

class Solution {
public:
    vector<vector<int>> res;
    vector<vector<int>> pathSum(TreeNode* root, int sum) {
         if(!root)
            return res;
        vector<int> tmp;
        pathSum1(root,sum,tmp);
         return res;
    }
    void pathSum1(TreeNode* root, int sum,vector<int> tmp)
    {
         if(!root)
            return ;
        vector<int> tmp1;
        tmp1 = tmp;
        tmp1.push_back(root->val);
        if(!root->left&&!root->right)
        {
            if(root->val==sum)
               res.push_back(tmp1);
            return;
        }
        pathSum1(root->left,sum-root->val,tmp1);pathSum1(root->right,sum-root->val,tmp1);
    }
};