Leetcode 75. Sort Colors

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本文深入探讨了三色排序算法，即彩虹排序的一种特例。通过三个指针划分数组为三个区域，实现原地排序。文章详细解释了根据不同颜色元素进行交换的条件，并附有完整的代码实现。

Problem:

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Analysis:

in place sort
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This question is actually a rainbow sort.
Since we have 3 colors, we will need 3 pointers to denote 3 districts.
It should be like the follows:

a a | b b | x x x | c c

a, b, c is three different color
x is the unknown color, which we need to explore in the next step.
we should know:
what if x== a, swap(nums[i], nums[j]), i++, j++
what if x== b , j++
what if x== c, swap(nums[k], nums[j]), k–

Note:

In the while() clause, try to figure out the corner case, j<k Or j<=k;
a easy way is to set a simple example.

Code:

public void sortColors(int[] nums) {
        
        if (nums == null || nums.length <= 1) return;
        
        int i = 0, j = 0, k = nums.length -1;
        while(j <= k){
            
            if(nums[j] == 1){
                j++;
            }else if (nums[j] == 0){               
                int temp = nums[j];
                nums[j] = nums[i];
                nums[i] = temp;
                i++;
                j++;               
            }else{
                int temp = nums[j];
                nums[j] = nums[k];
                nums[k] = temp;
                k--;
            }    
            
        }