[LeetCode] 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.

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.

这道题挺简单的，直接用recursive做就可以了。因为反正每一个node检查的方式都一样。

只要目前的sum减去正在检查的node的value之后等于0，就可以return true。

所以程序还是很简单的。

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public boolean hasPathSum(TreeNode root, int sum) {
if(root==null){
return false;
}
sum=sum-root.val;
if(root.left==null&&root.right==null){
if(sum==0){
return true;
}
return false;
}
return hasPathSum(root.left,sum)||hasPathSum(root.right,sum);
}
}