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.

分类：二叉树

题意：在二叉树中查找和为sum的路径(从根节点到叶子节点)

解法1：递归。由于sum可能是负数，所以必须遍历到根节点，过程中不能剪枝。

/**
* 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;
if(root.val==sum &&root.left==null&&root.right==null){
return true;
}else{
return hasPathSum(root.left, sum-root.val)||hasPathSum(root.right, sum-root.val);
}
}
}