PathSum.cpp

/*
  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.
*/

  /**
  * Definition for binary tree
  * 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;
    return pathHelper(root, sum);
  }
  bool pathHelper(TreeNode *root, int sum)
  {
    if(!root)
      return false;
    else
      {
	sum -= root->val;
	if(sum == 0 && !root->left && !root->right)
	  return true;
      }
    return pathHelper(root->left, sum) || pathHelper(root->right, sum);
  }
};