75. Sort Colors

难度: Medium

题目描述

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

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

You must solve this problem without using the library's sort function.

 

Example 1:

Input: nums = [2,0,2,1,1,0]
Output: [0,0,1,1,2,2]

Example 2:

Input: nums = [2,0,1]
Output: [0,1,2]

 

Constraints:

• n == nums.length
• 1 <= n <= 300
• nums[i] is either 0, 1, or 2.

 

Follow up: Could you come up with a one-pass algorithm using only constant extra space?

解题思路

代码实现

解决方案

java

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

    private void countSort(int[] nums) {
        int[] count = new int[3];
        for (int i = 0; i < nums.length; i++) {
            count[nums[i]]++;
        }
        int index = 0;
        for (int i = 0; i < count.length; i++) {
            int c = count[i];
            for (int j = 0; j < c; j++) {
                nums[index++] = i;
            }
        }
    }
}