排序算法之0-1、0-1-2排序

之前碰到个非常有意思的题目，是关于排序算法的题目：

已知：一个数组：array，数组元素：0或1或2

求解：将数组按照0-1-2排序？

template <class T>
void Swap(T& t1, T& t2)
{
    T tmp = t1;
    t1 = t2;
    t2 = tmp;
}

// Sorting a array which the elements are 0 or 1.
void SortArray_0_1(int* arr, int n)
{
    int first = 0;      // point to 0.
    int last = n - 1;   // point to 1.

    while (first < last)
    {
        // Find the position of first 0.
        while (0 == arr[first])
        {
            first++;
        }

        // Find the position of first 1.
        while (1 == arr[last])
        {
            last--;
        }

        if (first <= last && 1 == arr[first] && 0 == arr[last])
        {
            Swap(arr[first], arr[last]);
            first++;
            last--;
        }
    }
}

// Sorting a array which the elements are 0 or 1.
void SortArray2_0_1(int* arr, int n)
{
    //int first = 0;      // point to 0.
    int last = n - 1;   // point to 2.
    int k = 0;          // point to 1.

    while (k < last)
    {
        // Find 0.
        if (1 == arr[k])
        {
            while (1 == arr[last] && k < last)
            {
                last--;
            }

            if (k < last)
            {
                Swap(arr[k], arr[last]);
            }
        }

        if (0 == arr[k])
        {
            k++;
        }
    }
}

// Sorting a array which the elements are 0 or 1 or 2.
void SortArry_0_1_2(int* arr, int n)
{
    int first = 0;      // point to 0.
    int last = n - 1;   // point to 2.
    int k = 0;          // point to 1.

    while (k < last)
    {
        // Find 0.
        if (0 == arr[k])
        {
            while (0 == arr[first] && first < k)
            {
                first++;
            }

            if (first < k)
            {
                Swap(arr[k], arr[first]);
            }
        }

        // Find 1.
        if (1 == arr[k] || k == first)
        {
            k++;
        }

        // Find 2.
        if (2 == arr[k])
        {
            while (2 == arr[last] && k < last)
            {
                last--;
            }

            if (k < last)
            {
                Swap(arr[k], arr[last]);
            }
        }
    }
}