Question

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

Note: A leaf is a node with no children.

Difficulty:Medium

Category:Tree, Depth-First-Search

Analyze

So we use the template code for this Tree Question.

There are four steps for this template:

1. Boundary conditions.
2. Deal with the root value.
3. recursive call funciton
4. compare ouput value

Solution

/**
 * 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:
  bool hasPathSum(TreeNode* root, int sum) {
    if (!root) return false;
    if (!root->left && !root->right) return root->val == sum;
    bool l = hasPathSum(root->left, sum - root->val);
    bool r = hasPathSum(root->right, sum - root->val);
    return l || r;
  }
};