SCIP in C++11 ― 2.2.2節 その3

木の写像：問題2.30～2.31

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// tree-map

template<typename ReturnType, typename ArgType>

const List treeMap

(const function<ReturnType(ArgType)>& procedure,

 const List& listTree)

{

    if(isNull(listTree)){return(makeList());}

    if(!isPair(listTree)){

        return(leafMap(procedure,listTree));

    }

    return(cons(treeMap(procedure,car(listTree)),

                treeMap(procedure,cdr(listTree))));

}

//---------abstraction barrier---------

typedef int ListElementType;

typedef int FactorType;

const List scaleTree

(const List& listTree, const FactorType& factor)

{

    if(isNull(listTree)){return(makeList());}

    if(!isPair(listTree)){

        const function<FactorType(ListElementType)> factoring=

            [factor](const ListElementType x){return(factor*x);};

        return(leafMap(factoring,listTree));

    }

    return(cons(scaleTree(car(listTree),factor),

                scaleTree(cdr(listTree),factor)));

}

// for excersize 2.30

const function<ListElementType(ListElementType)>

square=[](const ListElementType x){return(x*x);};

const List squareTree_nonMap

(const List& listTree)

{

    if(isNull(listTree)){return(makeList());}

    if(!isPair(listTree)){return(leafMap(square,listTree));}

    return(cons(squareTree_nonMap(car(listTree)),

                squareTree_nonMap(cdr(listTree))));

}

// for excersize 2.31

const List squareTree(const List& tree)

{return(treeMap(square,tree));}

int main(int argc, char** argv)

{

    const auto tree1(makeList

                     (1,makeList(2,makeList(3,4),5),makeList(6,7)));

    cout<<"tree1 = "<<listString(tree1)<<endl;

    cout<<"(scale-tree tree1 10) = "

        <<listString(scaleTree(tree1,10))<<endl;

    cout<<endl<<"Excersize 2.30"<<endl;

    cout<<"(square-tree tree1) = "

        <<listString(squareTree_nonMap(tree1))<<endl;

    cout<<endl<<"Excersize 2.31"<<endl;

    cout<<"(square-tree tree1) = "

        <<listString(squareTree(tree1))<<endl;

    return(0);

}

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出力

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tree1 = (1 (2 (3 4) 5) (6 7))

(scale-tree tree1 10) = (10 (20 (30 40) 50) (60 70))

Excersize 2.30

(square-tree tree1) = (1 (4 (9 16) 25) (36 49))

Excersize 2.31

(square-tree tree1) = (1 (4 (9 16) 25) (36 49))