113. Path Sum II

• Difficulty: Medium

• Topics: Tree, Depth-first Search

• Similar Questions:

  • Path Sum

  • Binary Tree Paths

  • Path Sum III

  • Path Sum IV

Problem:

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]
]

Solutions:

/**
 * 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<int> path;
        vector<vector<int>> ret;

        helper(root, sum, path, ret);

        return ret;
    }

    void helper(TreeNode* root, int sum, vector<int>& path, vector<vector<int>>& ret) {
        if (root == nullptr)    return;
        if (root->left == nullptr && root->right == nullptr) {
            if (sum == root->val) {
                path.push_back(root->val);
                ret.push_back(path);
                path.pop_back();
            }
            return;
        }

        int val = root->val;
        path.push_back(val);
        helper(root->left, sum - val, path, ret);
        helper(root->right, sum - val, path, ret);
        path.pop_back();

        return;
    }
};