力扣530，为什么在网站上提交的输出和自己编译器上调试输出不一样

Question

问题遇到的现象和发生背景

刚刚开始用力扣，对力扣的执行机制不是很了解。调试语句输出和答案输出在两边都不一样。题目如下

问题相关代码，请勿粘贴截图

力扣代码：

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
min_abs = float('inf')
pre = None
class Solution:
    def getMinimumDifference(self, root: TreeNode) -> int:
        traversal(root)
        return min_abs
def traversal(root):
    global pre,min_abs
    if root is None:
        return
    # 中序遍历，求最小间隔
    traversal(root.left)  # 左
    if pre is not None:  # 中
        min_abs = min(abs(root.val-pre.val),min_abs)
    if pre is None: print("root is {}, pre is None".format(root.val))  # 调试语句
    else: print("root is {}, pre is {}".format(root.val, pre.val))
    pre = root
    traversal(root.right)  # 右
    

本地调试代码：

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right
min_abs = float('inf')
pre = None

def getMinimumDifference(root: TreeNode) -> int:
    traversal(root)
    return min_abs

def traversal(root):
    global pre,min_abs
    if root is None:
        return
    traversal(root.left)
    if pre is not None:
        min_abs = min(abs(root.val-pre.val),min_abs)
    if pre is None: print("root is {}, pre is None".format(root.val))
    else: print("root is {}, pre is {}".format(root.val, pre.val))
    pre = root
    traversal(root.right)

root = TreeNode(1)
right = TreeNode(5)
right.left = TreeNode(3)
root.right = right
ans = getMinimumDifference(root)
print(ans)

运行结果及报错内容

力扣输出：

本地输出：

Answer 1

是因为你测试的时候是单组数据，提交的时候是多组测试数据，你的min_abs是上次的结果，执行traversal，需要再次初始化全局变量

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
min_abs = float('inf')
pre = None
class Solution:
    def getMinimumDifference(self, root: TreeNode) -> int:
        
        global pre,min_abs
        min_abs = float('inf')  # 恢复一下初始化，因为是pre,min_abs是全局，多组测试数据情况下会使用上次的
        pre = None
        
        traversal(root)
        return min_abs
def traversal(root):
    global pre,min_abs
    if not root :
        return
    # 中序遍历，求最小间隔
    traversal(root.left)  # 左
    if   pre :  # 中
        min_abs = min(abs(root.val-pre.val),min_abs)
    pre = root
    traversal(root.right)  # 右