计算机问题求解 数据组织能力 算法设计能力 马骏 majun@nju.edu.cn
计算机问题求解 数据组织能力 算法设计能力 马骏 majun@nju.edu.cn
程序= Algorithms+ 数据结构+算法 Dafa Structures= Programs 数据与数据 解决特定问 之间的逻辑 题的步骤和 Niklaus Wirth 关系 方法 1984年图灵奖得主 Pascal之父" 多个编程语言的主设计师： 算法的操作对象是数据结构 Algol W Modula Pascal Modula-2 Oberon 数据结构是算法设计的基础
程序= 数据结构+算法 数据与数据 之间的逻辑 关系 解决特定问 题的步骤和 Niklaus Wirth 方法 • 1984年图灵奖得主 • “Pascal之父” • 多个编程语言的主设计师： • Algol W Modula Pascal Modula-2 Oberon 算法的操作对象是数据结构 数据结构是算法设计的基础
我们再来理解以下文字 What we are interested in are the ways algorithms can organize, remember,change,and access collections of data. While control structures serve to tell the processor where it should be going,data structures,and the operations upon them, organize the data items in ways that enable it to do whatever it should do when it gets there. 从理解数据结构的“结构”角度出发，哪些词最为关键？
我们再来理解以下文字 从理解数据结构的“结构”角度出发，哪些词最为关键？ What we are interested in are the ways algorithms can organize, remember, change, and access collections of data. While control structures serve to tell the processor where it should be going, data structures, and the operations upon them, organize the data items in ways that enable it to do whatever it should do when it gets there
抽象数据类型ADT一以栈为例 Out Out (LIFO)lists.Roughly,a stack is a set of objects which arrive at different points in time and are added to the set.When elements are deleted from the set, the object which was inserted last is removed first. A stack can be visualised as a pile of objects where objects can be added to or removed from the pile only from the top (see figure 2.3).In abstract terms,a Figure 2.3 Pictorial model of a stack
抽象数据类型ADT——以栈为例
栈的实现 单e●0● n s一-·T形 last Figure 3.2 Pointer representation of a stack S. Figure 2.6 Array implementation of stacks. 难道我们就定义了两个不同的stack了吗？
栈的实现 难道我们就定义了两个不同的stack了吗？
ADT stack:set of elements of type elemtype (elemtype is used to refer to the type of the individual elements in a stack. Elemtype can potentially be any defined type * Stack-ADT Operations: procedure initialise(var S:stack); This procedure assigns an empty stack to S. ·定义栈的管理动作： procedure push(var S:stack;a:elemtype); Stack S should not be full.This procedure adds the element a at ·initialize(S):创建一个栈； the top of the stack. ·push(S,c:将c压入栈S中： procedure pop(var S:stack); Stack S should not be empty.The top element of the stack is ·top(S):栈顶元素； removed. ·pop(S):将栈顶元素去除； function top(S:stack):elemtype; ·empty(S):判定S是否为空 Stack S should be non-empty and this function returns the top element of the stack S.The stack S is left unchanged.(If elem- ·ful(s:判断S是否满 type is a structured type,this function should be rewritten as a procedure,see note 1 of section 3.1.) function empty(S:stack):boolean; This function returns true if S is empty and false otherwise. function full(S stack):boolean; If S is full this function returns a true value. Otherwise it returns a false value
Stack-ADT • 定义栈的管理动作： • initialize(S):创建一个栈； • push(S,c):将c压入栈S中; • top(S):栈顶元素； • pop(S):将栈顶元素去除; • empty(S):判定S是否为空 • full(s):判断S是否满
如果我们在构造自己的数据组织方式时，写出 了一个关于这个方式的“约定”，而暂时没有 涉及实现细节，甚至不再关心实现细节而交由 其他人员实现时，我们写出来的“约定”就有 了新名词： 抽象数据类型：ADT
如果我们在构造自己的数据组织方式时，写出 了一个关于这个方式的“约定”，而暂时没有 涉及实现细节，甚至不再关心实现细节而交由 其他人员实现时，我们写出来的“约定”就有 了新名词： 抽象数据类型：ADT
ADT stack:set of elements of type elemtype (elemtype is used to refer to the type of the individual elements in a stack. Elemtype can potentially be any defined type + Operations: procedure initialise(var S:stack); This procedure assigns an empty stack to S. procedure push(var S:stack;a:elemtype); 完整的 Stack S should not be full.This procedure adds the element a at the top of the stack. stack的 procedure pop(var S:stack); Stack S should not be empty.The top element of the stack is ADT removed. function top(S stack):elemtype; Stack S should be non-empty and this function returns the top element of the stack S.The stack S is left unchanged.(If elem- type is a structured type,this function should be rewritten as a procedure,see note 1 of section 3.1.) function empty(S:stack):boolean; This function returns true if S is empty and false otherwise. function full(S:stack):boolean; If S is full this function returns a true value. Otherwise it returns a false value
完整的 stack的 ADT
自然语言能够描述清楚ADT中各个成分吗？ Finally,since ADTs are mathematical objects,their meaning can be formally specified.Based on these specifications,it is then possible to verify that a given implementation of an ADT is correct and agrees with the specification. 狭义的程序设计中难得一见的科学内涵！
自然语言能够描述清楚ADT中各个成分吗？ 狭义的程序设计中难得一见的科学内涵！
Stack的数据部分的形式约束 stack::c integer (current time-point * max integer (maximum allowable size * 规约的数 据部分 elems pair-set (elems is a set of pairs * pair :object elemtype (object is of type elemtype * integer (t is a time-stamp * invariance 1:not [3a,b,t (a,t)eelems and (b,t)∈elems and 针对数据 的规约 a≠b] 生命周期 内保持 invariance 2:V(a,t)E elems c>t invariance 3:I elemsl max
Stack的数据部分的形式约束 针对数据 的规约 生命周期 内保持 规约的数 据部分