leetcode || 75、Sort Colors

最新推荐文章于 2025-12-21 17:04:13 发布

原创最新推荐文章于 2025-12-21 17:04:13 发布 · 904 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#leetcode #快速排序 #双指针 #算法

LeetCode 专栏收录该内容

131 篇文章

订阅专栏

本文介绍了一种在不使用字典排序的情况下，通过一次遍历完成数组排序的方法，特别适用于由0、1、2组成的数组。通过设置三个指针分别用于处理0、1、2元素，实现高效排序。

problem：

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.

click to show follow up.

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?

Hide Tags

Array Two Pointers Sort

题意：将由0、1、2组成的数组按升序排序，不能使用字典排序

thinking：

（1）最简单的是使用计数法，计算0、1、2 的个数，最后再填充

（2）最优算法是快速排序的变形：一次遍历完成排序

code：

class Solution {
public:
    void sortColors(int A[], int n) {
        int i = 0; // 0 pointer
        int j = n - 1; // 1 pointer
        int k = n - 1; // 2 pointer
        
        while (i <= j)
        {
            if (A[i] == 2)
            {
                int t = A[k];
                A[k] = A[i];
                A[i] = t;
                k--;
                if (k < j)
                    j = k;
            }
            else if (A[i] == 1)
            {
                int t = A[j];
                A[j] = A[i];
                A[i] = t;
                j--;
            }
            else
                i++;
        }
    }
};