75

class Solution {
public:
    void sortColors(vector<int>& nums) {
        int n=nums.size(), last, first;
        last = n-1; first = 0;
        for(int i=0; i<n; i++){
            while(nums[i] == 2 && i<last) swap(nums[i], nums[last--]);
            while(nums[i] == 0 && i>first) swap(nums[i], nums[first++]);
        }
    }
};