[LeetCode] 75. Sort Colors

[LeetCode] 75. Sort Colors

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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.

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?

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其實就是對一串0s, 1s, 2s排序。。。
思路： 既然固定了元素，直接桶排序，就是統計0、1、2的個數，再順序輸出。

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class Solution {
public:
    void sortColors(vector<int>& nums) {
        vector<int> bucket(3, 0);
        int len = nums.size();
        for (int i=0; i<len; ++i) {
            ++bucket[nums[i]];
        }
        int k = 0;
        for (int i=0; i<3; ++i) {
            for (int j=0; j<bucket[i]; ++j) {
                nums[k++] = i;
            }
        }
    }
};