​LeetCode刷题实战530：二叉搜索树的最小绝对差

class Solution {
    // 二叉搜索树的最小绝对差
    int min_diff = Integer.MAX_VALUE;
    int pre = -1;
    public int getMinimumDifference(TreeNode root) {
        // 中序遍历
        if(root==null){
            return min_diff;
        }
        // 左根右
        getMinimumDifference(root.left);
        if(pre!=-1){
            min_diff = Math.min(Math.abs(root.val-pre),min_diff);
            pre = root.val;
        }else{
            pre = root.val;
        }

        getMinimumDifference(root.right);
        return min_diff;
    }
}