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Commit b751418

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add 剑指OFFER 03
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‎python basic/in2post.py‎

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#==================================================
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#==> Title: 中缀 --> 后缀
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#==> Author: Zhang zhen
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#==> Email: hustmatnoble.gmail.com
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#==> GitHub: https://github.com/MatNoble
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#==> Date: 2/20/2021
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#==================================================
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# coding:utf-8
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def priority(z):
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if z in [×ばつ', '*', '/']:
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return 2
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elif z in ['+', '-']:
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return 1
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def in2post(expr):
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""" :param expr: 中缀表达式
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:return: 后缀表达式
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Example:
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"1+((2+3)×ばつ4)-5"
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"1 2 3 + 4 ×ばつ + 5 -"
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"""
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stack = [] # 存储栈
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post = [] # 后缀表达式存储
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for z in expr:
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if z not in [×ばつ', '*', '/', '+', '-', '(', ')']: # 数字直接输出
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post.append(z)
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else:
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if z != ')' and (not stack or z == '(' or stack[-1] == '('
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or priority(z) > priority(stack[-1])): # stack 不空;栈顶为(;优先级大于
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stack.append(z) # 运算符入栈
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elif z == ')': # 右括号出栈
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while True:
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x = stack.pop()
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if x != '(':
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post.append(x)
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else:
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break
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else: # 比较运算符优先级,看是否入栈出栈
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while True:
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if stack and stack[-1] != '(' and priority(z) <= priority(stack[-1]):
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post.append(stack.pop())
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else:
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stack.append(z)
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break
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while stack: # 还未出栈的运算符,需要加到表达式末尾
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post.append(stack.pop())
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return post
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# if __name__ == '__main__':
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s = "1+((2+3)×ばつ4)-5"
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post = in2post(s)
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print('后缀表达式: ',post)

‎test.py‎

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#==================================================
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#==> Title:
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#==> Author: Zhang zhen
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#==> Email: hustmatnoble.gmail.com
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#==> GitHub: https://github.com/MatNoble
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#==> Date:
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#==================================================
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while True:
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try:
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from collections import Counter
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n = int(input())
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nums = list(map(int, input()))
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if n & 1:
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i, j = n//2 - 1, n//2 + 1
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else:
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i, j = n//2 - 1, n//2
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d = Counter(nums)
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dl = Counter(nums[:i+1])
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dr = Counter(nums[j:])
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res = dl[0] + dr[1] # 左 1 右 0
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res0 = d[1] # 全 0
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res1 = d[0] # 全 1
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print(min(res, res0, res1))
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except:
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break

‎剑指offer/README.md‎

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## 剑指 Offer 题解
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> Python 版本
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[LeetCode 网站版](https://leetcode-cn.com/problemset/lcof/)
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<hr />
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### 数组、字符串
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<img src="https://cdn.jsdelivr.net/gh/MatNoble/Images/20210327102030.png" title="数组、字符串"/>

‎剑指offer/offer03.ipynb‎

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{
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"metadata": {
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.8.5-final"
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},
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"orig_nbformat": 2,
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"kernelspec": {
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"name": "python3",
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"display_name": "Python 3.8.5 64-bit",
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"metadata": {
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"interpreter": {
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"hash": "31f2aee4e71d21fbe5cf8b01ff0e069b9275f58929596ceb00d14d90e3e16cd6"
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}
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}
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}
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},
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"nbformat": 4,
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"nbformat_minor": 2,
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"cells": [
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{
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"source": [
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"找出数组中重复的数字。\n",
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"\n",
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"在一个长度为 $n$ 的数组 `nums` 里的所有数字都在 0ドル〜n-1$ 的范围内。数组中某些数字是重复的,但不知道有几个数字重复了,也不知道每个数字重复了几次。请找出数组中任意一个重复的数字。\n",
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"\n",
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"示例 1: \n",
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"输入:$[2, 3, 1, 0, 2, 5, 3]$ \n",
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"输出:2ドル$ 或 3ドル$ \n",
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" \n",
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"限制: \n",
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"2ドル \\leq n \\leq 100000$\n",
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"\n",
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"来源:力扣(LeetCode) \n",
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"链接:https://leetcode-cn.com/problems/shu-zu-zhong-zhong-fu-de-shu-zi-lcof \n",
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"著作权归领扣网络所有。商业转载请联系官方授权,非商业转载请注明出处。"
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],
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"cell_type": "markdown",
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"metadata": {}
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},
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{
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"source": [
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"### 计数法\n",
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"\n",
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"借助 [Counter 模块](https://matnoble.me/tech/programming/python/collections/#counter) `计数`,返回`计数`最多的数"
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],
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"cell_type": "markdown",
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"metadata": {}
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"metadata": {},
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"outputs": [],
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"source": [
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"from collections import Counter \n",
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"class Solution:\n",
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" def findRepeatNumber(self, nums):\n",
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" # 计数法\n",
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" return Counter(nums).most_common(1)[0][0]"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 2,
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"metadata": {},
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"outputs": [
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{
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"output_type": "execute_result",
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"data": {
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"text/plain": [
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"2"
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]
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},
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"metadata": {},
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"execution_count": 2
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}
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],
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"source": [
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"# 测试\n",
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"nums = [2, 3, 1, 0, 2, 5, 3]\n",
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"mat = Solution()\n",
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"mat.findRepeatNumber(nums)"
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]
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},
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{
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"source": [
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"### 哈希表\n",
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"\n",
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"用`哈希表`查找元素,时间复杂度$O(1)$"
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],
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"cell_type": "markdown",
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"metadata": {}
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},
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{
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"cell_type": "code",
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"execution_count": 3,
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"metadata": {},
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"outputs": [],
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"source": [
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"class Solution:\n",
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" def findRepeatNumber(self, nums):\n",
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" # 哈希表\n",
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" d = set()\n",
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" for num in nums:\n",
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" if num in d: return num\n",
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" d.add(num)"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 4,
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"metadata": {},
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"outputs": [
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{
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"output_type": "execute_result",
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"data": {
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"text/plain": [
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"2"
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]
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},
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"metadata": {},
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"execution_count": 4
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}
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],
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"source": [
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"# 测试\n",
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"nums = [2, 3, 1, 0, 2, 5, 3]\n",
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"mat = Solution()\n",
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"mat.findRepeatNumber(nums)"
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]
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},
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{
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"source": [
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"### 原地置换 环\n",
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"\n",
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"<img src=\"https://cdn.jsdelivr.net/gh/MatNoble/Images/20210327105657.png\" width=400/>"
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],
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"cell_type": "markdown",
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"metadata": {}
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},
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{
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"cell_type": "code",
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"execution_count": 5,
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"metadata": {},
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"outputs": [],
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"source": [
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"class Solution:\n",
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" def findRepeatNumber(self, nums):\n",
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" # 原地置换 环\n",
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" i = 0\n",
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" while i < len(nums):\n",
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" if nums[i] == i: \n",
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" i += 1\n",
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" continue\n",
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" if nums[nums[i]] == nums[i]: \n",
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" return nums[i] # 返回环入口\n",
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" # swap i <- -> j\n",
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" j = nums[i]\n",
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" nums[i], nums[j] = nums[j], nums[i]"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 6,
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"metadata": {},
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"outputs": [
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{
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"output_type": "execute_result",
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"data": {
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"text/plain": [
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"2"
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]
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},
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"metadata": {},
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"execution_count": 6
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}
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],
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"source": [
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"# 测试\n",
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"nums = [2, 3, 1, 0, 2, 5, 3]\n",
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"mat = Solution()\n",
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"mat.findRepeatNumber(nums)"
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]
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}
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]
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}

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