/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
int maxAncestorDiff(TreeNode* root) {
if(!root) return -1;
int val = root->val;
return max(dfs(root->left, val, val), dfs(root->right, val, val));
}
int dfs(TreeNode* root, int minv, int maxv) {
if(!root) return -1;
int val = root->val;
//这里maxv和minv的语句位置不影响结果,因为第一次更新result与位置无关
int result = max(abs(val - minv), abs(val - maxv));
maxv = max(maxv, val);
minv = min(minv, val);
result = max(result, dfs(root->left, minv, maxv));
result = max(result, dfs(root->right, minv, maxv));
return result;
}
};