LeetCode 75 Sort Colors (思维)

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#思维

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本文深入探讨了经典的三色排序问题，即荷兰国旗问题。通过一个直观且高效的单遍算法，实现了不同颜色对象的相邻排序，确保颜色顺序为红、白、蓝。文章详细解释了算法的工作原理，包括如何使用两个指针来跟踪不同颜色的位置，以及如何在常数空间复杂度下实现一过排序。此外，还提供了LeetCode上该题目的0ms解决方案。

Given an array with n objects colored red, white or blue, sort them in-place 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.

Example:

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

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 a one-pass algorithm using only constant space?

题目链接：https://leetcode.com/problems/sort-colors/

题目分析：经典问题，当前位置为2和末尾交换后指针不后移，因为若末尾为0或2，还需对当前位置进行二次置换

0ms，时间击败100%

class Solution {
    
    public void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }
    
    public void sortColors(int[] nums) {
        int left = 0, right = nums.length - 1, i = 0;
        while (i <= right) {
            if (nums[i] == 2) {
                swap(nums, i, right--);
            } else if (nums[i] == 0) {
                swap(nums, left++, i++);
            } else {
                i++;
            }
        }
    }
}