[leetcode]112. Path Sum路径和(是否有路径)

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.

题意：

给定二叉树和一个值，判断从根到叶是否存在一条路径，其路径和等于该值。

思路：

dfs

代码：

 class Solution {
     public boolean hasPathSum(TreeNode root, int sum) {
         if(root == null) return false;

         if(root.left== null && root.right== null)
             return root.val == sum; 

         if(hasPathSum(root.left, sum - root.val))
             return true;
         if(hasPathSum(root.right, sum - root.val))
             return true;

         return false;
     }
 }