常用函数实现

求最大公约数

int gcd(int a, int b)
{
    if (a == 0 || b == 0)
        return 0;
    int tmp = 0;
    while (b != 0)
    {
        tmp = b;
        b = a%b;
        a = tmp;
    }
    return a;
}

交换swap

template <class T>
void swap(T &a, T &b)
{
    T c(std::move(a));
    a = std::move(b);
    b = std::move(c);
}

   a = a ^ b;
    b = a ^ b;
    a = a ^ b;

 

求某个区间随机数

int RandomlnRange()
{
    if (start > end)
        return -1;
    return rand() % (end - start + 1) + start;
}

分割数组Partition

int Partition_v1(vector<int>& num, int low, int high)
{
    int pivot = num[low];
    while (low < high)
    {
        while (low < high && num[high] >= pivot)
            --high;
        num[low] = num[high];
        while (low < high && num[low] <= pivot)
            ++low;
        num[high] = num[low];
    }
    num[low] = pivot;
    return low;
}

 

分解质因数（面试题考过）

void Analyse(int n)
{
    //打印出  
    int i;
    for (i = 2; i <= sqrt(static_cast<double>(n)); i++)
    {
        if (n % i == 0)
        {
            n = n / i;
            cout << i << "*";
            i--;
        }
    }
    cout << n << endl;

}

 

不用加号计算两数和

int add(int a, int b)
{
    if (b == 0)
        return a;
    int sum = a^b;
    int carry = (a&b) << 1;
    return add(sum, carry);
}

strcpy

char *strcpy(char *strDest, const char *strSrc)
{
    assert(strDest != NULL && strSrc != NULL);
    char *address = strDest;
    while ((*strDest++ = *strSrc++) != '\0');
    return address;
}

二分查找

 #include <iostream>

using namespace std;

/*
*二分查找思想：1、数组从小到大排序；2、查找的key每次和中间数比较，如果key小于mid
查找mid左侧的数组部分；如果key大于mid，则查找mid右侧的数组部分；如果相等，则直接返回mid。

输入：排序数组-array,数组大小-aSize,查找值-key
返回：返回数组中的相应位置，否则返回-1
*/
//非递归查找
int BinarySearch(int *array, int aSize, int key)
{
    if ( array == NULL || aSize == 0 )
        return -1;
    int low = 0;
    int high = aSize - 1;
    int mid = 0;

    while ( low <= high )
    {
        mid = (low + high )/2;
        
        if ( array[mid] < key)
            low = mid + 1;
        else if ( array[mid] > key )   
            high = mid - 1;
        else
            return mid;
    }
    return -1;
}
//递归
int BinarySearchRecursive(int *array, int low, int high, int key)
{
    if ( low > high )
        return -1;
    int mid = ( low + high )/2;
    
    if ( array[mid] == key )
        return mid;
    else if ( array[mid] < key )
        return BinarySearchRecursive(array, mid+1, high, key);
    else
        return BinarySearchRecursive(array, low, mid-1, key);
}

int main()
{
    int array[10];
    for (int i=0; i<10; i++)
        array[i] = i;

    cout<<"No recursive:"<<endl;
    cout<<"position:"<<BinarySearch(array, 10, 6)<<endl;
    cout<<"recursive:"<<endl;
    cout<<"position:"<<BinarySearchRecursive(array, 0, 9, 6)<<endl;

    return 0;
}