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  • Orange Boy Can You Solve It Out? Ep. 65
    OBCYSIO

    Orange Boy Can You Solve It Out? Ep. 65

    Solved Difficulty: D2C 思考题 inspired by Saionji Video Channel Eastmost Eki There are n points on a 2D plane. You can select any real point as pivot in the rectangle bounded by (a,b) and (c,d) and rotate the entire plane by d degree clockwis……
    XGN 2025年8月24日
  • Orange Boy Can You Solve It Out? Ep. 64
    OBCYSIO

    Orange Boy Can You Solve It Out? Ep. 64

    思考题 inspired by car lanes Car Lane In Ryuto the capital of the Dragon Kingdom, there is an intersection with k+1 exits. On one lane of one exit, there is a queue of n cars. The i-th car in the queue wants to go in the direction d_i (1\leq d_i\le……
    XGN 2025年8月23日
  • Orange Boy Can You Solve It Out? Ep. 63
    OBCYSIO

    Orange Boy Can You Solve It Out? Ep. 63

    Solved Difficulty: D2C-D2D 思考题 inspired by Create Mod Assembly Line There is an assembly line consisting of n machines. The i-th machine on the line holds an infinitely long input queue and a processing time of t_i seconds. The machines wo……
    XGN 2025年8月23日
  • Orange Boy Can You Solve It Out? Ep. 62
    OBCYSIO

    Orange Boy Can You Solve It Out? Ep. 62

    short 思考题 A^B Problem Given two pattern strings A and B that consists of lower-case letters, ? (match a single character) and * (match one or more characters) For example, abc?d*e matches abcfdppe and abcgde but not ae or abcdde. Find a string t……
    XGN 2025年1月2日
  • crimboi[22] 你什么拓扑?
    教程

    crimboi[22] 你什么拓扑?

    funny problem from model theory problem sheet 题面 Let L be a countable language, T a theory. Let c_1,c_2,... be new constants, L'=L\cup\lbrace c_1,...\rbrace, and let X be the set of all complete theories of L' with T\subset t. Enumerate the L' se……
    HDD 2024年11月15日
  • crimboi[21] 模仿大赛
    教程

    crimboi[21] 模仿大赛

    Rotman algebraic topology上的题, 个人认为出的非常好, 极大增进了读者对\pi_1(S^1)计算过程的理解. 题面 A group G which is also a topology space is called a topological group if \mu:G\times G\to G:(x,y)\mapsto xy and i:G\to G:x\mapsto x^{-1} are contin……
    HDD 2024年9月14日
  • Orange Boy Can You Solve It Out? Ep. 61
    OBCYSIO

    Orange Boy Can You Solve It Out? Ep. 61

    思考题 featuring Hikari again! Guess the string Hikari and her master Ninetail are playing a game. Hikari thinks of a string S with lower-case letters, and Ninetail asks her to make q modifications one by one. Each modification can only be one of t……
    XGN 2024年9月4日
  • crimboi[20] 泛函分析心犯寒
    教程

    crimboi[20] 泛函分析心犯寒

    Dieudonne的题, 真实难度不好说, 回顾一下发现其实挺简单的. 题面 Let E be a Hilbert space, F a dense linear subspace of E, distinct from E. (For example E space of l^2 sum of a suitable countable linear independent set and F space of finite sum of thi……
    HDD 2024年8月1日
  • crimboi[19] 吃屎绕大弯
    教程

    crimboi[19] 吃屎绕大弯

    题目背景 为证一个非零吃大师 题面 Assuming AC, prove that for a integral domain R, if any nonzero prime ideal P contains a nonzero prime (p), R is UFD. 先想再看提示哦 提示 Let S be the set of elements that are prime factori……
    HDD 2024年7月6日
  • 2024春南京大学大学物理期末考试题目速报(Prof. Yachong Guo)
    题&解

    2024春南京大学大学物理期末考试题目速报(Prof. Yachong Guo)

    概括 原文为英文,本文是回忆版,具体数据可能有误。考完收试卷、草稿纸。可以携带一张A4手写笔记。不可以带计算器。 期中传送门 120分钟5题. P1 有一根长为2a的均匀杆子竖立在光滑水平面上,由于扰动开始倒下,问: 快接触地面时的角速度 快接触地面时的质心速度 P……
    XGN 2024年6月25日