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版权声明：本文为博主原创文章，转载请注明出处：http://blog.jerkybible.com/2013/09/18/2013-09-18-CODE 21 Path Sum/

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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.

public boolean hasPathSum(TreeNode root, int sum) {
	// Start typing your Java solution below
	// DO NOT write main() function
	if (null == root) {
		return false;
	}
	return dfs(root, 0, sum);
}

private boolean dfs(TreeNode root, int current, int sum) {
	if (root.left == null && root.right == null) {
		if (current + root.val == sum) {
			return true;
		} else {
			return false;
		}
	}
	boolean is = false;
	if (root.left != null) {
		is = dfs(root.left, current + root.val, sum);
	}
	if (is) {
		return is;
	}
	if (root.right != null) {
		is = dfs(root.right, current + root.val, sum);
	}
	return is;
}