leetcode_530二叉搜索树的最小绝对差值

中序遍历，右下持续递增，判断当前值和上一个值的差值即可

var getMinimumDifference = function(root) {
 let ans = Number.MAX_SAFE_INTEGER, pre = -1;
    const dfs = (root) => {
        if (root === null) {
            return;
        }
        dfs(root.left);
        if (pre == -1) {
            pre = root.val;
        } else {
            ans = Math.min(ans, root.val - pre);
            pre = root.val;
        }
        dfs(root.right);
    }
    dfs(root);
    return ans;
};js