leetcode: Sort Colors

最新推荐文章于 2022-02-07 13:25:19 发布

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本文介绍了一种不使用标准库排序函数就能实现的三色排序算法。该算法将数组中的元素按红、白、蓝三种颜色排序，分别用整数0、1、2表示。通过巧妙地使用三个指针，该算法能有效地将相同颜色的元素相邻放置，并保持颜色顺序。

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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.

class Solution {
    
    void swap(int A[], int i, int j)
    {
        int tmp = A[i];
        
        A[i] = A[j];
        A[j] = tmp;
    }
    
public:
    void sortColors(int A[], int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (!A || n == 0)
            return;
    
        int redPos;
        int whitePos;
        int bluePos;
        
        redPos  = whitePos = 0;
        bluePos = n-1;
        
        while (whitePos <= bluePos)
        {
            if (A[whitePos] == 0)
            {
                swap(A, whitePos, redPos);
                redPos++;
                whitePos++;
            }
            else if (A[whitePos] == 2)
            {
                swap(A, whitePos, bluePos);
                bluePos--;
            }
            else
            {
                whitePos++;
            }
        }    
    }
};