Leetcode Problem 112 Path Sum.txt

112. Path Sum

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.

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.

Hint To Solve: Use recursion for tree problems. Caution a node with no children is only considered as a left node. Edge case [1,2] with sum 1 should considered false.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    
    public bool HasPathRecursive(TreeNode root, int targetSum, int currentSum)
    {
        if(root == null)
            return false;
        
        if(root.left == null && root.right == null)
        {
            if(currentSum + root.val == targetSum)
                return true;
            else
                return false;
        }
        
        return HasPathRecursive(root.left, targetSum, root.val+currentSum) || HasPathRecursive(root.right,targetSum, root.val+currentSum);
    }
    
    public bool HasPathSum(TreeNode root, int sum) 
    {
        return HasPathRecursive(root,sum, 0);
    }
}