leetcode-75-Sort Colors

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?

void sortColors(vector<int>& nums) {
    int zero =0, l = 0, r = nums.size()-1;
    while (l <= r) {
        if (nums[l] == 0) 
            swap(nums[l++], nums[zero++]);
        else if (nums[l] == 2) 
            swap(nums[l], nums[r--]);
        else
            l++;
    }
}