Question

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,

Difficulty:Medium

Category:Tree, Depth-first Search

Analyze

Solution

//Runtime: 8ms
class Solution {
 public:
  vector<vector<int>> pathSum(TreeNode* root, int sum) {
    vector<vector<int>> ans;
    vector<int> cur;
    dfs(root, sum, cur, ans);
    return ans;
  }

 private:
  void dfs(TreeNode* root, int sum, vector<int>& cur, vector<vector<int>>& ans) {
    if (!root) return;
    if (!root->left && !root->right) {
      if (root->val == sum) {
        cur.push_back(root->val);
        ans.push_back(cur);
        cur.pop_back();
      }
      return;
    }
    cur.push_back(root->val);
    dfs(root->left, sum - root->val, cur, ans);
    dfs(root->right, sum - root->val, cur, ans);
    cur.pop_back();
  }
};