128_leetcode_Sort Colors

1:

Given an array with n objects colored red, white or blue, sort them so that objects of the same color are adjacent, with the colors in the order red, white and blue.

Here, we will use the integers 0, 1, and 2 to represent the color red, white, and blue respectively.

Note:
You are not suppose to use the library's sort function for this problem.

1:注意特殊情况；2:遍历数组一次；3:设置两个指针，分别表示0和2的边界，当从头到后遍历数组的时候，如果是1，直接遍历下一个；如果为0，与前面的数组进行交换；如果是2， 与后面的数字进行交换，注意循环结束的情况

    void sortColors(int A[], int n)
    {
        if(A == NULL || n <= 1)
        {
            return;
        }
        
        int leftIndex = -1;
        int rightIndex = n;
        int i = 0;
        
        while(i < rightIndex)
        {
            if(A[i] == 1 || i == leftIndex)
            {
                i++;
            }
            else if(A[i] == 0)
            {
                int tmp = A[i];
                A[i] = A[++leftIndex];
                A[leftIndex] = tmp;
            }
            else if(A[i] == 2)
            {
                int tmp = A[i];
                A[i] = A[--rightIndex];
                A[rightIndex] = tmp;
            }
        }
        return;
    }