• Question
• Solution

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.

For example:

Given the below binary tree and sum = 22,

              5
             / \
            4   8
           /   / \
          11  13  4
         /  \      \
        7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

Solution

Result: Accepted Time: 8 ms

Here should be some explanations.

bool hasPathSum(struct TreeNode* root, int sum) {
    if(root == NULL)
        return false;
    if(root -> left == NULL && root->right == NULL)
        return root->val == sum;
    return hasPathSum(root->left,sum-root->val) || hasPathSum(root->right,sum-root->val);
}

Complexity Analytics

• Time Complexity: $O(n)$
• Space Complexity: $O(1)$