[LeetCode]Sort Colors

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 ++;
        }
    }

    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 ++;
            }
        }

    }

[LeetCode]Sort Colors

原文：http://blog.csdn.net/youmengjiuzhuiba/article/details/44900249