Re: [問題] 面試問到的問題...

[Leon (Achilles)]

※ 引述《Leon (Achilles)》之銘言：
: : 接著說明一下直線截成線段的問題。
: : 對偶的時候，點(a,b)對偶成直線y=ax+b。
: : 考慮兩個直線的交點，也就是兩條直線解聯立方程式。
: : 根據公式解，交點的座標範圍一定會在 |a|*|b|+|c|*|d| 之內。
:
: First, I don't understant your notation.
: What do you mean by the range |a|*|b|+|c|*|d| ?
:
: It seems not a range in 2D ?
:
:
: And I have the same question for you.
:
: Assume you have N lines, based on your description
: You claim there is a range for the intersection.
:
: Then, how many operations you need to calculate the range?
:
:
: --
: ※ 發信站: 批踢踢實業坊(ptt.cc)
: ◆ From: 142.136.127.136
: 推 DJWS:(1) 我指的是 Cramer's rule 那些係數                        12/13 15:39
: → DJWS:(2) N個頂點對偶成直線, N條直線各自截成N條線段 ---> O(N)    12/13 15:40
: → DJWS:另外我是假設座標都是整數  如果座標-1<0<1那麼範圍就會更大   12/13 15:41

OK, I really doubt your writing..

Linear algebra 001, high school algebra

intersection of two lines.

y = ax + b ;
y = cx + d ;

ax + b = cx + d ;

(a-c)x = d - b ;
x = (d-b) / (a-c) ;

Now, please tell me how it is related to your |a|*|b|+|c|*|d|
from Cramer's rule?

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※ 發信站: 批踢踢實業坊(ptt.cc) 
◆ From: 142.136.127.136
推 DJWS:恩 你說的沒錯  那麼範圍最大到 |d|+|b| 才對
→ Leon:you are wrong again, look, there is (a-c) term!
推 DJWS:恩 你說的沒錯　除非abcd都是整數　範圍才是 |d|+|b|
→ Leon:then revise your post. Everyone should be responsible to
→ Leon:what they write
推 DJWS:這是當然 XD
→ Leon:OK, your first statement is wrong. Now you can answer
→ Leon:the second question: