◻️75. Sort Colors (Dutch National Flag Problem) (medium)

Given an array nums 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.

We will use the integers 0, 1, and 2 to represent the color red, white, and blue, respectively.

You must solve this problem without using the library's sort function.

Example 1:

Input: nums = [2,0,2,1,1,0]
Output: [0,0,1,1,2,2]

Example 2:

Input: nums = [2,0,1]
Output: [0,1,2]

---

Solutions

Optimised using While loop - Std. soln

Runtime 0 ms Memory 10.16 MB

```cpp
// Standard code by chatgpt

class Solution {
public:
    void sortColors(vector<int>& nums) {
         int l = 0, mid = 0, r = nums.size() - 1;
    
        while (mid <= r) {
            if (nums[mid] == 0) {
                swap(nums[l++], nums[mid++]);
            } else if (nums[mid] == 1) {
                mid++;
            } else { // nums[mid] == 2
                swap(nums[mid], nums[r--]);
            }
        }
    }
};
```

Optimised using For loop

Runtime 0 ms Memory 10.07 MB

// corrected using chatGPT

class Solution {
public:
    void sortColors(vector<int>& nums) {
        int n=nums.size();
        int l=0, r=n-1;
        for (int i = 0; i <= r; ++i) {
            if (nums[i] == 0 && i > l) {
                swap(nums[i--], nums[l++]); // Decrement i to recheck the swapped value
            } else if (nums[i] == 2) {
                swap(nums[i--], nums[r--]); // Decrement i to recheck the swapped value
            }
        }
    }
};