Path Sum

【问题描述】

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.

【解决方案】

/**
 * Definition for binary tree
 * struct TreeNode {
 * int val;
 * struct TreeNode *left;
 * struct TreeNode *right;
  * };
 */
bool hasPathSum(struct TreeNode *root, int sum) {
    if(NULL == root)
    {
        return false;
    }

    if(NULL == root->left && NULL == root->right)
    {
        return sum == root->val;
    }

    return hasPathSum(root->left, sum - root->val)
            || hasPathSum(root->right, sum - root->val);
}