Maximal Amplitude of a Binary Tree

maxAmp.cpp

class TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int val_) : val(val_) {}
};

class Solution {
    int ans = 0;
    int maxAmp(struct TreeNode* root) {
        if (root == NULL) return 0;
        helper(root, root->val, root->val);
        return ans;
    }
    void helper(struct TreeNode* root, int min_val, int max_val) {
        if (root == NULL) return 0;
        min_val = min(min_val, root->val);
        max_val = max(max_val, root->val);
        ans = max(ans, max_val - min_val);
        helper(root->left, min_val, max_val);
        helper(root->right, min_val, max_val);
    }
};