day16-day18代码片段

1. 二叉树的层序遍历

void _LevelOrder(Node *pRoot)
    {
        Node *pCur = pRoot;
        queue<Node *> q;
        q.push(pCur);
        while (!q.empty())
        {
            Node *pTop = q.front();
            cout << pTop->_data << " ";
            q.pop();
            if (pTop->_pLeft)
                q.push(pTop->_pLeft);
            if (pTop->_pRight)
                q.push(pTop->_pRight);
        }
    }

2. 判断树是否是完全二叉树

bool _IsCompleteTree(Node *pRoot)
    {
        if (pRoot == nullptr)
            return true;
        queue<Node *> q;
        Node *pCur = pRoot;
        q.push(pCur);
        bool flag = false;
        while (!q.empty())
        {
            Node *pTop = q.front();
            q.pop();
            if (flag&&pTop->_pLeft || pTop->_pRight)
                return false;
            if (pTop->_pLeft == nullptr&&pTop->_pRight != nullptr)
                return false;
            if (pTop->_pLeft)
                q.push(pTop->_pLeft);
            if (pTop->_pRight)
                q.push(pTop->_pRight);
            else
                flag = true;
        }
        return true;
    }

3. 判断是否是二叉树的后续遍历

bool IsPostOrder(int sequence[], int length)
{
    if (sequence == nullptr || length <= 0)
        return false;
    int root = sequence[length - 1];
    int i = 0;
    for (; i < length-1; ++i)
    {
        if (sequence[i]>root)
            break;
    }
    int j = i;
    for (; j < length - 1; ++j)
    {
        if (sequence[i] < root)
            return false;
    }
    bool left = true;
    if (i>0)
        left = IsPostOrder(sequence, i);
    bool right = true;
    if (i < length - 1)
        right = IsPostOrder(sequence + i, length - i - 1);
    return left&&right;

}

4. 打印二叉树中和为某一值的路径

void _FindPath(Node *pRoot, int expectData, int Sum, vector<int> &path)
{
    Sum += pRoot->_data;
    path.push_back(pRoot->_data);
    bool isLeaf = pRoot->_pLeft == nullptr&&pRoot->_pRight == nullptr;
    if (isLeaf&&Sum == expectData)
    {
        printf("find the path\n");
        vector<int>::iterator it = path.begin();
        for (; it != path.end(); it++)
        {
            printf("%d\t", *it);
        }
        printf("\n");
    }
    if (pRoot->_pLeft)
        _FindPath(pRoot->_pLeft, expectData, Sum, path);
    if (pRoot->_pRight)
        _FindPath(pRoot->_pRight, expectData, Sum, path);
    //递归退出时记得清理栈
    path.pop_back();

}

5. 二叉搜索树转双向链表

//注意pre用引用
void _ToList(Node *pRoot, Node *&pre)
    {
        if (NULL==pRoot)
            return;
        Node *cur = pRoot;
        _ToList(pRoot->_pLeft,pre);
        if (pre)
        {
            pre->_pRight = cur;
        }
        cur->_pLeft = pre;
        pre = cur;
        _ToList(pRoot->_pRight,pre);
    }

6. 复杂链表的复制

void CloneNode(ListNode *pHead)
{
    ListNode *pNode = pHead;
    while (pNode != nullptr)
    {
        ListNode *pCloned = new ListNode;
        pCloned->_data = pNode->_data;
        pCloned->_pNext = pNode->_pNext;
        pCloned->_pSibling = nullptr;
        pNode->_pNext = pCloned;
        pNode = pCloned->_pNext;
    }
}
void CloneSibling(ListNode *pHead)
{
    ListNode *pNode = pHead;
    while (pNode != nullptr)
    {
        ListNode *pCloned = pNode->_pNext;
        if (pNode->_pSibling != nullptr)
        {
            pCloned->_pSibling = pNode->_pSibling->_pNext;
        }
        pNode = pCloned->_pNext;
    }
}
ListNode *DivideList(ListNode *pHead)
{
    ListNode *pNode = pHead;
    ListNode *pCloneHead = nullptr;
    ListNode *pCloneNode = nullptr;
    if (pNode != nullptr)
    {
        pCloneHead = pNode->_pNext;
        pNode->_pNext = pCloneHead->_pNext;
        pNode->_pNext = pNode->_pNext;
    }
    while (pNode != nullptr)
    {
        pCloneNode->_pNext = pNode->_pNext;
        pCloneNode = pCloneNode->_pNext;
        pNode->_pNext = pCloneNode->_pNext;
        pNode = pNode->_pNext;
    }
    return pCloneHead;
}

7. 寻找数组中出现次数大于一半的数字

#include<iostream>
using namespace std;
bool flag = false;
int partion(int *arr, int length, int left, int right)
{
    int key = arr[left];
    int start = left;
    int end = right - 1;
    while (start < end)
    {
        while(start < end&&arr[end] >=key)
            end--;
        while (start < end&&arr[start] <= key)
            ++start;
        if (start < end)
            swap(arr[start], arr[end]);
    }
    swap(arr[start], arr[left]);
    return start;
}
bool CheckLegal(const int *arr, int length)
{
    flag = false;
    if (arr == nullptr || length <= 0)
        flag = true;
    return flag;
}
bool resLegal(int *arr, int length, int res)
{
    int times = 0;
    for (int i = 0; i < length; i++)
    {
        if (arr[i] == res)
            times++;
    }
    if (times * 2 < length)
        return false;
    return true;
}
int MoreThanNum(int *arr, int length)
{
    if (CheckLegal(arr, length))
    {
        return 0;
    }
    int mid = length >> 1;
    int start = 0;
    int end = length - 1;
    int index = partion(arr, length, start, end);
    while (index != mid)
    {
        if (index > mid)
        {
            end = index - 1;
            index = partion(arr, length, start, end);
        }
        else
        {
            start = index + 1;
            index = partion(arr, length, start, end);
        }
    }
    int res = arr[mid];
    if (!resLegal(arr, length, res))
        res = 0;
    return res;
}
int Find(int *arr, int length)
{
    if (arr == nullptr || length < 1)
        return 0;
    int res = arr[0];
    int times = 0;
    for (int i = 0; i < length; i++)
    {
        if (times == 0)
        {
            res = arr[i];
            times = 1;
        }
        else if (arr[i] == res)
            ++times;
        else
            --times;
    }
    if (!resLegal(arr, length, res))
        res = 0;
    return res;
}
void test()
{
    int arr[] = { 1, 4, 5, 2, 2, 2,2};
    cout << Find(arr, sizeof(arr) / sizeof(arr[0]));
}
int main()
{
    test();
    system("pause");
}

8. 字符串全排列

#include<iostream>
using namespace std;
void range(char *str, char *pBegin)
{
    if (*pBegin == '\0')
        cout << str << endl;
    else
    {
        for (char *pCh = pBegin; *pCh != '\0'; pCh++)
        {
            swap(*pCh, *pBegin);
            range(str, pBegin + 1);
            swap(*pCh, *pBegin);
        }
    }
}
int main()
{
    char arr[] = "abc";
    range(arr, arr);
    system("pause");
    return 0;
}