leetcode530. Minimum Absolute Difference in BST

平衡二叉樹的性質。

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int fi=1;
    int m=2147483647;
    int last=0;
    void f(TreeNode* root){
       if(root==NULL)  return ;
        f(root->left);
        if(fi){ last=root->val; fi=0; }
        else{ m=min(m,abs(last-root->val)); last=root->val; }
        f(root->right);
    }
    int getMinimumDifference(TreeNode* root) {
        f(root);
        return m;
    }
};