LeetCode 113. Path Sum II

Posted 2020-10-10

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]
]

/**
 * 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) {
        vector<vector<int>> res;
        if (!root) return res;
        vector<int> out;
        helper(res, out, sum, root);
        return res;
    }
    void helper(vector<vector<int>>& res, vector<int>& out, int sum, TreeNode *node) {
        if (!node) return;
        out.push_back(node->val);
        if (sum == node->val && !node->left && !node->right) res.push_back(out);
        
        sum = sum - node->val;
        if (node->left) helper(res, out, sum, node->left);
        if (node->right) helper(res, out, sum, node->right);

        out.pop_back();
    }
};