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.

              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.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    boolean flag=false;
    public boolean hasPathSum(TreeNode root, int sum) {
        if(root==null) return flag;
        isTrue(root,sum);
        return flag;
    }
    public void isTrue(TreeNode root, int sum){
        if(root==null) return;
        if(root.right==null && root.left==null && sum-root.val==0) flag=true;
        else {
            isTrue(root.left,sum-root.val);
            isTrue(root.right,sum-root.val);
        }
    }
    
}

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