Equal Tree Partition

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

int preCalculate(TreeNode* V) {
    int sum = V->val;
    if (V->left) sum += preCalculate(V->left);
    if (V->right) sum += preCalculate(V->right);
    return sum;
}
int isPossible(TreeNode* V, int& total, int& possible) {
    int sum = V->val;
    if (V->left) sum += isPossible(V->left, total, possible);
    if (V->right) sum += isPossible(V->right, total, possible);
    if (2*sum == total) possible = 1;
    return sum;
}
int Solution::solve(TreeNode* A) {
    int sum = preCalculate(A), possible = 0;
    isPossible(A, sum, possible);
    return possible;
}