179179 < li class ="toctree-l2 "> < a href ="#python-int "> python int 值范围</ a > </ li >
180180
181181
182- < li class ="toctree-l2 "> < a href ="#python-listdict "> python list/dict 排序等技巧</ a > </ li >
182+ < li class ="toctree-l2 "> < a href ="#python_2 "> python 负数位运算的坑</ a > </ li >
183+
184+
185+ < li class ="toctree-l2 "> < a href ="#python-list "> python list 技巧</ a > </ li >
186+
187+
188+ < li class ="toctree-l2 "> < a href ="#python-dict "> python dict 技巧</ a > </ li >
183189
184190
185191 < li class ="toctree-l2 "> < a href ="#_2 "> 链表题目调试函数</ a > </ li >
188194 < li class ="toctree-l2 "> < a href ="#_3 "> 内置库实现优先级队列的三种方式</ a > </ li >
189195
190196
191- < li class ="toctree-l2 "> < a href ="#python_2 "> python 如何实现最大堆</ a > </ li >
197+ < li class ="toctree-l2 "> < a href ="#python_3 "> python 如何实现最大堆</ a > </ li >
192198
193199
194200 < li class ="toctree-l2 "> < a href ="#lru_cachecache "> lru_cache/cache 优化记忆化搜索</ a > </ li >
197203 < li class ="toctree-l2 "> < a href ="#leetcode "> leetcode 二叉树调试函数</ a > </ li >
198204
199205
200- < li class ="toctree-l2 "> < a href ="#python_3 "> python 交换列表元素的坑</ a > </ li >
206+ < li class ="toctree-l2 "> < a href ="#python_4 "> python 交换列表元素的坑(交换副作用) </ a > </ li >
201207
202208
203209 < li class ="toctree-l2 "> < a href ="#acm "> 兼容代码ACM/核心提交格式</ a > </ li >
@@ -341,7 +347,7 @@ <h1 id="python_1">python 递归暴栈(栈溢出)</h1>
341347sys.setrecursionlimit(100000) # 设置函数栈深度足够大，避免栈溢出错误
342348</ code > </ pre >
343349< h1 id ="python-int "> python int 值范围</ h1 >
344- < pre > < code > # 乘方 （比较推荐，py2/3 都兼容不容易出错)
350+ < pre > < code > # 乘方 （比较推荐⭐️ ，py2/3 都兼容不容易出错)
345351MAXINT = 2**63-1
346352MININT = -2**63
347353
@@ -357,18 +363,23 @@ <h1 id="python-int">python int 值范围</h1>
357363MAXINT = (1<<63) - 1
358364MININT = ~MAXINT
359365</ code > </ pre >
360- < h1 id ="python-listdict "> python list/dict 排序等技巧</ h1 >
361- < pre > < code class ="language-py "> # python 根据 key，value 排序字典
362- d = {'d': 4, 'a': 1, 'b': 2, 'c':3}
363- # dict sort by key and reverse
364- dict(sorted(d.items())) # {'a': 1, 'b': 2, 'c': 3, 'd': 4}
365- dict(sorted(d.items(), reverse=True)) # {'d': 4, 'c': 3, 'b': 2, 'a': 1}
366-
367- # dict sort by value and reverse
368- dict(sorted(d.items(), key = lambda kv:kv[1])) # {'a': 1, 'b': 2, 'c': 3, 'd': 4}
369- dict(sorted(d.items(), key = lambda kv:kv[1], reverse=True)) # {'d': 4, 'c': 3, 'b': 2, 'a': 1}
370-
371- # 排序嵌套 list
366+ < h1 id ="python_2 "> python 负数位运算的坑</ h1 >
367+ < ol >
368+ < li > Python3 中的整型是补码形式存储的</ li >
369+ < li > Python3 中 bin 一个负数（十进制表示），输出的是它的原码的二进制表示加上个负号</ li >
370+ < li > 为了获得负数（十进制表示）的补码，需要手动将其和十六进制数 0xffffffff 进行按位与操作，得到结果是个十六进制数，再交给 bin() 进行输出，
371+ 得到的才是你想要的补码表示。</ li >
372+ </ ol >
373+ < pre > < code class ="language-py "> # 整数转换 https://leetcode-cn.com/problems/convert-integer-lcci/
374+ class Solution:
375+ def convertInteger(self, A: int, B: int) -> int:
376+ return bin((A & 0xffffffff) ^ (B & 0xffffffff)).count('1')
377+ </ code > </ pre >
378+ < p > 参考：
379+ - https://www.runoob.com/w3cnote/python-negative-storage.html
380+ - https://leetcode-cn.com/problems/convert-integer-lcci/solution/python3-zhu-yi-qi-dui-yu-fu-shu-de-cun-chu-fang-sh/</ p >
381+ < h1 id ="python-list "> python list 技巧</ h1 >
382+ < pre > < code class ="language-py "> # 排序嵌套 list
372383l = [('a', 1), ('c', 2), ('b',3)]
373384sorted(l, key=lambda p:p[0]) # 根据第1个值排序，[('a', 1), ('b', 3), ('c', 2)]
374385sorted(l, key=lambda p:p[1]) # 根据第2个值排序，[('a', 1), ('c', 2), ('b', 3)]
@@ -377,25 +388,44 @@ <h1 id="python-listdict">python list/dict 排序等技巧</h1>
377388l = [1,2,5,4,3]
378389maxi, maxval = max(enumerate(l), key=lambda iv: iv[1]) # 2, 5
379390
380- # 获取字典对应的最大值对应的 key,value
381- mydict = {'A':4,'B':10,'C':0,'D':87}
382- maximum = max(mydict, key=mydict.get) # Just use 'min' instead of 'max' for minimum.
383- maxk, maxv = maximum, mydict[maximum]
384- # 或者
385- maxk, maxv = max(mydict.items(), key=lambda k: k[1])
386-
387- # python3 排序list自定义函数(python2 直接用 cmp 参数)
391+ # python3 排序list自定义函数(python2 直接用 cmp 参数， python3 需要用 cmp_to_key 转成 key 参数)
388392from functools import cmp_to_key
389393nums = [3,2,1,4,5]
390- sorted(nums, key= cmp_to_key(lambda a,b: a-b) ) # [1 ,2 ,3, 4, 5]
391- sorted(nums, key= cmp_to_key(lambda a,b: b-a) ) # [5, 4, 3, 2, 1]
394+ sorted(nums, key=cmp_to_key(lambda a,b: a-b) ) # [1 ,2 ,3, 4, 5]
395+ sorted(nums, key=cmp_to_key(lambda a,b: b-a) ) # [5, 4, 3, 2, 1]
392396
393397# 一行代码判断列表是否有序
394398issorted = all(l[i] <= l[i+1] for i in range(len(l) - 1))
395399
396400# python3 一行代码求前缀和
397401from itertools import accumulate
398402presums = list(accumulate([1,2,3])) # [1, 3, 6]
403+
404+ # 一行代码求矩阵元素总和 https://stackoverflow.com/questions/10713150/how-to-sum-a-2d-array-in-python
405+ allsum = sum(map(sum, matrix)) # 或者 allsum = sum((sum(row) for row in matrix))
406+ </ code > </ pre >
407+ < h1 id ="python-dict "> python dict 技巧</ h1 >
408+ < pre > < code class ="language-py "> # python 根据 key，value 排序字典
409+ d = {'d': 4, 'a': 1, 'b': 2, 'c':3}
410+ # dict sort by **key** and reverse
411+ dict(sorted(d.items())) # {'a': 1, 'b': 2, 'c': 3, 'd': 4}
412+ dict(sorted(d.items(), reverse=True)) # {'d': 4, 'c': 3, 'b': 2, 'a': 1}
413+
414+ # dict sort by **value** and reverse
415+ dict(sorted(d.items(), key = lambda kv:kv[1])) # {'a': 1, 'b': 2, 'c': 3, 'd': 4}
416+ dict(sorted(d.items(), key = lambda kv:kv[1], reverse=True)) # {'d': 4, 'c': 3, 'b': 2, 'a': 1}
417+
418+ # 获取字典对应的最大值对应的 key,value
419+ mydict = {'A':4,'B':10,'C':0,'D':87}
420+ maximum = max(mydict, key=mydict.get) # Just use 'min' instead of 'max' for minimum.
421+ maxk, maxv = maximum, mydict[maximum]
422+ # 或者
423+ maxk, maxv = max(mydict.items(), key=lambda k: k[1])
424+
425+ # 支持默认值的有序字典 (OrderedDict and defaultdict)
426+ # https://stackoverflow.com/questions/6190331/how-to-implement-an-ordered-default-dict
427+ od = OrderedDict() # collections.OrderedDict()
428+ od[i] = od.get(i, 0) + 1 # 间接实现了 defaultdict(int) ，同时保持了插入字典的 key 顺序
399429</ code > </ pre >
400430< h1 id ="_2 "> 链表题目调试函数</ h1 >
401431< pre > < code class ="language-py "> # 编写链表题目经常用到的一些通用函数和调试函数，定义等，方便代码调试
@@ -512,7 +542,7 @@ <h1 id="_3">内置库实现优先级队列的三种方式</h1>
512542 while pq:
513543 print(heapq.heappop(pq))
514544</ code > </ pre >
515- < h1 id ="python_2 "> python 如何实现最大堆</ h1 >
545+ < h1 id ="python_3 "> python 如何实现最大堆</ h1 >
516546< p > python自带了heapq 模块实现了最小堆(min-heaq)，但是如果想要实现最大堆(max-heap)，有几种实现方式：</ p >
517547< ol >
518548< li > 对放入的数字取反。比如 10 放入 -10 ，然后取出来的时候再取反。个人倾向于这种，可以自己封装一个类防止来回取反搞晕</ li >
@@ -705,7 +735,7 @@ <h1 id="leetcode">leetcode 二叉树调试函数</h1>
705735 cur.right = right
706736 return root
707737</ code > </ pre >
708- < h1 id ="python_3 "> python 交换列表元素的坑</ h1 >
738+ < h1 id ="python_4 "> python 交换列表元素的坑(交换副作用) </ h1 >
709739< pre > < code > # 41. 缺失的第一个正数 https://leetcode-cn.com/problems/first-missing-positive/
710740class Solution(object):
711741 def firstMissingPositive(self, nums):
@@ -725,7 +755,7 @@ <h1 id="python_3">python 交换列表元素的坑</h1>
725755 while 1 <= nums[i] <= n and nums[nums[i]-1] != nums[i]:
726756 # NOTE: 注意这一句交换右边有副作用的，不能颠倒！！！
727757 # nums[i], nums[nums[i]-1] = nums[nums[i]-1], nums[i] # 这么写死循环！
728- nums[nums[i]-1], nums[i] = nums[i], nums[nums[i]-1]
758+ nums[nums[i]-1], nums[i] = nums[i], nums[nums[i]-1] # 有副作用的放前边
729759 for i in range(n):
730760 if nums[i] != i+1:
731761 return i+1
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