/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

* TreeNode(int x) { val = x; }

* }

*/

// time : O(n);

// space : O(n);

class Solution {

public boolean hasPathSum(TreeNode root, int sum) {

if(root == null) return false;// to detect root is null or giving an option for later excuting if either one of root.left and root.right is null.

if(root.left == null && root.right == null) return sum == root.val;

//checking when u hitting each path to the end.

return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val); // excuting the one is true;

}

public boolean hasPathSum(TreeNode root, int sum) {

if(root == null) return false;

Stack<TreeNode> stack = new Stack<>();

stack.push(root);

while(!stack.isEmpty()){

TreeNode cur = root;

cur = stack.pop();

if(cur.left == null && cur.right == null){

if(sum == cur.val) return true;

}

if(cur.left != null) {

stack.push(cur.left);

cur.left.val += cur.val;

}

if(cur.right != null) {

stack.push(cur.right);

cur.right.val += cur.val;

}

}

return false;

}

}