Check for Children Sum Property in a Binary Tree

class Solution{
    public:
    //Function to check whether all nodes of a tree have the value 
    //equal to the sum of their child nodes.
    bool p=1;
    void solve(Node* root){
        if(root==NULL) return ;
        if(root->left==NULL&& root->right==NULL) return ;
        int sum1=0;
        if(root->left!=NULL) sum1+=root->left->data;
        if(root->right!=NULL) sum1+=root->right->data;
        if(root->data!=sum1) p=0;
        solve(root->left);
        solve(root->right);
        
    }
    int isSumProperty(Node *root)
    {
        solve(root);
        return p; 
    }
};