Path Sum

1.题目

判断是否从根到叶子的路径和跟给定sum相同的

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.

2.算法

用递归法，看看左子树或右子树有没有满足条件的路径

public boolean hasPathSum(TreeNode root, int sum) {
if(root == null)
return false;
if(root.left == null && root.right==null && root.val==sum)
return true;
return hasPathSum(root.left, sum-root.val) || hasPathSum(root.right, sum-root.val);
}