旋轉(zhuǎn)環(huán)形天線

《航?？萍济~》第一版。

1996年，經(jīng)全國科學(xué)技術(shù)名詞審定委員會(huì)審定發(fā)布。

兩棵二叉樹之間的旋轉(zhuǎn)距離指的是, 其中一棵樹通過盡可能少的樹旋轉(zhuǎn)變換到另一棵樹, 此過程中所使用的旋轉(zhuǎn)次數(shù). 對(duì)于一個(gè)包含相同個(gè)數(shù)節(jié)點(diǎn)的二叉樹集合, 它們兩兩之間的距離可以構(gòu)成一個(gè)度量空間. 是否存在一個(gè)算法, 能在多項(xiàng)式時(shí)間內(nèi)計(jì)算兩個(gè)二叉樹之間的旋轉(zhuǎn)距離, 目前還是一個(gè)未決問題。

基于旋轉(zhuǎn)油缸的小身材，強(qiáng)力和可靠性不可能被感知到。最強(qiáng)大的HKS擺動(dòng)缸可將20輛大眾Golf轎車從一邊轉(zhuǎn)到另一邊。這一設(shè)計(jì)是建立在帶有多重螺旋齒輪的系統(tǒng)之上的。通過多重螺旋齒輪將活塞的直線運(yùn)動(dòng)轉(zhuǎn)化成旋轉(zhuǎn)運(yùn)動(dòng)?；钊闹本€運(yùn)動(dòng)越長(zhǎng)，旋轉(zhuǎn)運(yùn)動(dòng)就越大。

樹旋轉(zhuǎn)包括兩個(gè)不同的方式，分別是右旋轉(zhuǎn)（以P為轉(zhuǎn)軸）和左旋轉(zhuǎn)（以Q為轉(zhuǎn)軸）。兩種旋轉(zhuǎn)呈鏡像，而且互為逆操作。

下圖示意了兩種樹旋轉(zhuǎn)過程中, 子樹的初態(tài)和終態(tài)：

 ---  --- 
|Q||P|
 ---  --- 
/\rightrotation/\
 ---  --- -------------> ---  --- 
|P||Z||X||Q|
 ---  --- <------------- ---  --- 
/\leftrotation/\
 ---  ---  ---  --- 
|X||Y||Y||Z|
 ---  ---  ---  --- 

其中, 右旋轉(zhuǎn)詳細(xì)步驟如下圖 R0, R1, R2 三個(gè)步驟所示, 左旋轉(zhuǎn)則如 L0, L1, L2 三個(gè)步驟所示。

__
/\
 --- / --- 
|Q|/|Q|
 ---  ---  --- / --- 
 --- |P|/\R1|P|//\ --- 
|Q|R0 --- / --- -----> --- / --- R2|P|
 --- ----->/\/|Z|//|Z|-----> --- 
/\ ---  ---  ---  ---  ---  --- /\
 ---  --- |X||Y||X||Y| ---  --- 
|P||Z| ---  ---  ---  --- |X||Q|
 ---  --- __ ---  --- 
/\/\/\
 ---  --- L2 --- \ --- L0 ---  --- 
|X||Y|<-----|P|\|P|<-----|Y||Z|
 ---  ---  --- \ --- L1 ---  ---  ---  --- 
/\\|Q|<-----/\|Q|
 --- \ ---  --- \ --- 
|X|\\|X|\/\
 ---  ---  ---  ---  ---  --- 
|Y||Z||Y||Z|
 ---  ---  ---  ---