lec_8.cpp

class Solution {
    public:
        void sortColors(vector<int>& arr) {
    
            int n = arr.size();
    
            int low = 0 , mid = 0 , high = n-1;
    
            while(mid<= high){
    
                if(arr[mid] == 0){
                    swap(arr[low] , arr[mid]);
                    low++;
                    mid++;
                }
                else if(arr[mid] == 1){
                    mid++;
                }
                else {
    
                    swap(arr[mid] , arr[high]);
                    high--;
                }
            }
        }
    };