Leetcode(Sort Colors )

最新推荐文章于 2019-05-21 15:41:52 发布

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最新推荐文章于 2019-05-21 15:41:52 发布

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分类专栏： c++ LeetCode 面试题文章标签：面试 leetcode color

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本文介绍了一种不使用库排序函数的颜色排序算法。该算法通过遍历数组并调整索引位置来确保相同颜色的对象相邻且按红、白、蓝的顺序排列。文章详细解释了算法的工作原理，并提供了一个使用C++实现的示例。

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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.

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?

代码：

class Solution {
public:
    void sortColors(int A[], int n) {
        int zero_idx = 0;
        int two_idx = n - 1;
        while(A[zero_idx] == 0)
            ++zero_idx;
        while(A[two_idx] == 2)
            --two_idx;
        int i = zero_idx;
        while(i <= two_idx)
        {
            if(A[i] == 1)
               ++i;
            else if(A[i] == 0)
            {
                if(i == zero_idx)
                   ++i;
                else 
                   swap(A[i], A[zero_idx]);
                ++zero_idx;
            }
            else
            {
                swap(A[i], A[two_idx]);
                --two_idx;
            }
        }   
    }
};