[LeetCode]Sort Colors

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.

思路1：直接遍历数组统计三种颜色的个数然后依次填充，复杂度O（N）

代码1：

    public void sortColors1(int[] A) {//统计1,2,3的个数        int [] colorCount = new int[3];        for(int i =0; i < A.length; ++i){            switch (A[i]){                case 0: colorCount[0] ++; break;                case 1: colorCount[1] ++; break;                case 2: colorCount[2] ++; break;            }        }        int from, i = 0, to = 0;        while (i < colorCount.length){            from = to;            to = to + colorCount[i];            Arrays.fill(A, from ,to,i);            i ++;        }    }

思路2：模拟快排，将2和0分别移动到两边，这只需要遍历一次数组即可，算法复杂度O(N)
代码2:

    public void sortColors(int[] A) {//用快速排序的思想，        final int RED = 0, WHITE = 1, BLUE = 2;        int l =0, r = A.length - 1,mid = l;        while (mid <= r){            if(A[mid] == RED){                int temp = A[mid];                A[mid] = A[l];                A[l] = temp;                l ++;                mid ++;            }else if(A[mid] == BLUE){                int temp = A[mid];                A[mid] = A[r];                A[r] = temp;                r --;            }else {                mid ++;            }        }    }