C++ 基础题目

1.赋值运算符函数

对于数组：

 const Stack & Stack::operator(const Stack & rightHandSide
 
{
     
     if(this != &rightHandSide)
     {
        delete[] myArray;
        myCapacity=rightHandSide.myCapacity;
        myArray=new StackElement[myCapacity];
        if (myArray ==0)
        {
            cerr<<"Indequate memory";
            exit(1);
        }
     }
     myTop=rightHandSide.myTop;
     for (int pos=0; pos<=myTop;pos++)
     {
         myArray[pos]=rightHandSide.myArray[pos];
     }
     return *this;
 }

对于字符串：

 CMyString& CMyString::operator = (const CMyString& str)

{
    if(this == &str)
        return *this;

    delete []m_pData;
    m_pData = nullptr;

    m_pData = new char[strlen(str.m_pData) + 1];
    strcpy(m_pData, str.m_pData);

    return *this;
}

2.数组中重复的数字

bool duplicate(int numbers[], int length, int* duplication)
{
   
    if(numbers == nullptr || length <= 0)
        return false;

    for(int i = 0; i < length; ++i)
    {
        if(numbers[i] < 0 || numbers[i] > length - 1)
            return false;
    }

    for(int i = 0; i < length; ++i)
    {
        while(numbers[i] != i)
        {
            if(numbers[i] == numbers[numbers[i]])
            {
                *duplication = numbers[i];
                return true;
            }

            // 交换numbers[i]和numbers[numbers[i]]             
            int temp = numbers[i];
            numbers[i] = numbers[temp];
            numbers[temp] = temp;
        }
    }

    return false;
}

3. 不修改数组找出重复的数字

int getDuplication(const int* numbers, int length)
{
    if(numbers == nullptr || length <= 0)
        return -1;

    int start = 1;
    int end = length - 1;
    while(end >= start)
    {
        int middle = ((end - start) >> 1) + start;
        int count = countRange(numbers, length, start, middle);
        if(end == start)
        {
            if(count > 1)
                return start;
            else
                break;
        }

        if(count > (middle - start + 1))
            end = middle;
        else
            start = middle + 1;
    }
    return -1;
}


int countRange(const int* numbers, int length, int start, int end)
{
    if(numbers == nullptr)
        return 0;

    int count = 0;
    for(int i = 0; i < length; i++)
        if(numbers[i] >= start && numbers[i] <= end)
            ++count;
    return count;
}

4. 二维数组的查找 一维数组模型

bool Find(int* matrix, int rows, int columns, int number)
{
    bool found = false;

    if(matrix != nullptr && rows > 0 && columns > 0)
    {
        int row = 0;
        int column = columns - 1;
        while(row < rows && column >=0)
        {
            if(matrix[row * columns + column] == number)
            {
                found = true;
                break;
            }
            else if(matrix[row * columns + column] > number)
                -- column;
            else
                ++ row;
        }
    }

    return found;
}

5.替换空格 从后往前复制

void ReplaceBlank(char str[], int length)
{
    
    if(str == nullptr && length <= 0)
        return;

    /*originalLength 为字符串str的实际长度*/
    int originalLength = 0;
    int numberOfBlank = 0;
    int i = 0;
    while(str[i] != '\0')
    {
        ++ originalLength;

        if(str[i] == ' ')
            ++ numberOfBlank;

        ++ i;
    }

    /*newLength 为把空格替换成'%20'之后的长度*/
    int newLength = originalLength + numberOfBlank * 2;
    if(newLength > length)
        return;

    int indexOfOriginal = originalLength;
    int indexOfNew = newLength;
    while(indexOfOriginal >= 0 && indexOfNew > indexOfOriginal)
    {
        if(str[indexOfOriginal] == ' ')
        {
            str[indexOfNew --] = '0';
            str[indexOfNew --] = '2';
            str[indexOfNew --] = '%';
        }
        else
        {
            str[indexOfNew --] = str[indexOfOriginal];
        }

        -- indexOfOriginal;
    }
}

6.重建二叉树

BinaryTreeNode* Construct(int* preorder, int* inorder, int length)
{
    if(preorder == nullptr || inorder == nullptr || length <= 0)
        return nullptr;

    return ConstructCore(preorder, preorder + length - 1,
        inorder, inorder + length - 1);
}


BinaryTreeNode* ConstructCore
(
    int* startPreorder, int* endPreorder, 
    int* startInorder, int* endInorder
)

{
    // 前序遍历序列的第一个数字是根结点的值
    int rootValue = startPreorder[0];
    BinaryTreeNode* root = new BinaryTreeNode();
    root->m_nValue = rootValue;
    root->m_pLeft = root->m_pRight = nullptr;

    if(startPreorder == endPreorder)
    {
        if(startInorder == endInorder && *startPreorder == *startInorder)
            return root;
        else
            throw std::exception("Invalid input.");
    }

    // 在中序遍历中找到根结点的值
    int* rootInorder = startInorder;
    while(rootInorder <= endInorder && *rootInorder != rootValue)
        ++ rootInorder;

    if(rootInorder == endInorder && *rootInorder != rootValue)
        throw std::exception("Invalid input.");

    int leftLength = rootInorder - startInorder;
    int* leftPreorderEnd = startPreorder + leftLength;
    if(leftLength > 0)
    {
        // 构建左子树
        root->m_pLeft = ConstructCore(startPreorder + 1, leftPreorderEnd, 
            startInorder, rootInorder - 1);
    }
    if(leftLength < endPreorder - startPreorder)
    {
        // 构建右子树
        root->m_pRight = ConstructCore(leftPreorderEnd + 1, endPreorder,
            rootInorder + 1, endInorder);
    }

    return root;
}