Sort Colors

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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.

Follow up:
A rather straight forward solution is a two-pass algorithm using counting sort.
First, iterate the array counting number of 0’s, 1’s, and 2’s, then overwrite array with total number of 0’s, then 1’s and followed by 2’s.

Could you come up with an one-pass algorithm using only constant space?

描述

给出一堆 0，1，2，将其排序，要求不使用已有的排序函数，并且其复杂度为 O(n)

分析

因为只有 0，1，2 三类数字组成，所以遍历的过程中，将 0 放在前方，将 2 放在后方

代码

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public class Solution {
    public void sortColors(int[] nums) {

        int n = nums.length;
        int l = 0, r = n - 1;

        for (int i = 0; i <= r; i++) {

            if (nums[i] == 0) {
                nums[i] = nums[l];
                nums[l++] = 0;

            } else if (nums[i] == 2) {
                nums[i] = nums[r];
                nums[r--] = 2;
                i--;
            }
        }
    }
}