113.Path Sum II

Tags: Medium Tree Depth-first Search

Links: https://leetcode.com/problems/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]
]

---

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> pathSum(TreeNode* root, int sum) {
        std::ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        cout.tie(NULL);

        vector<vector<int>> res;
        vector<int> tmp;
        DFS(root, sum, tmp, res);
        return res;
    }

    void DFS(TreeNode *root, int sum, vector<int> & tmp, vector<vector<int>> &res)
    {
        if (!root) return;
        tmp.push_back(root -> val);
        if (root -> val == sum && !root -> left && !root -> right) 
            res.push_back(tmp);

        DFS(root -> left, sum - root -> val, tmp, res);
        DFS(root -> right, sum - root -> val, tmp, res);
        tmp.pop_back();
    }
};