LeetCode: Path Sum

LeetCode: Path Sum 

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/**
 * Created by hzhou on 4/22/15. [email protected]
 */
public class PathSum {
    public boolean hasPathSum(TreeNode root, int sum) {
        if (root == null) {
            return false;
        }
        return helper(root, sum);
    }
    private boolean helper(TreeNode root, int sum) {
        if (root != null && root.left == null && root.right == null) {
            return sum == root.val;
        }
        boolean left = false;
        boolean right = false;
        assert root != null;
        if (root.left != null) {
            left = helper(root.left, sum - root.val);
        }
        if (root.right != null) {
            right = helper(root.right, sum - root.val);
        }
        return left || right;
    }
}