Path Sum

题目
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.

答案

class Solution {
    public boolean hasPathSum(TreeNode root, int sum) {
        if(root == null) return false;
        return recur(root, sum, 0);
    }
    
    private boolean recur(TreeNode root, int sum, int mysum) {
        if(root.left == null && root.right == null) {
            return sum == mysum + root.val;
        }
        boolean l = false, r = false;
        if(root.left != null)
            l = recur(root.left, sum, mysum + root.val);
        if(root.right != null)
            r = recur(root.right, sum, mysum + root.val);
        return l || r;
    }
}