Leetcode 112 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.

Solution 1: Recursive DFS

 public class Solution {  
   public boolean hasPathSum(TreeNode root, int sum) {  
     return dfs(root,0,sum);  
   }  
   private boolean dfs(TreeNode x, int num, int sum) {  
     if (x==null) return false;  
     if (x.left==null && x.right==null) {  
       if (num+x.val==sum) return true;  
       else return false;  
     }  
     return dfs(x.left,num+x.val,sum) || dfs(x.right,num+x.val,sum);  
   }  
 }  

Solution 2: Iterative DFS.

 public class Solution {  
   public boolean hasPathSum(TreeNode root, int sum) {  
     Deque<TreeNode> s1=new LinkedList<>();  
     Deque<Integer> s2=new LinkedList<>();  
     TreeNode x=root;  
     int num=0;  
     while (x!=null || !s1.isEmpty()) {  
       if (x!=null) {  
         num+=x.val;  
         s1.push(x);  
         s2.push(num);  
         x=x.left;  
       }  
       else {  
         x=s1.pop();  
         num=s2.pop();  
         if (x.left==null && x.right==null && num==sum) return true;  
         x=x.right;  
       }  
     }  
     return false;  
   }  
 }