Leetcode problems

#1


Please help me to solve this problems.

#2

You can solve it using two pointer approach.

void sortColors(vector<int>& nums) {

    // all numbers before nums[l] are 0
    // all numbers after nums[r] are 2
    int l = 0, r = nums.size() - 1;
    int i = 0;
    while(i <= r){
        if(nums[i] == 1) ++i;
        else if(nums[i] == 0){
            //swap(nums[l++], nums[i++]);
            nums[i++] = nums[l];
            nums[l++] = 0;
        }else{
            //swap(nums[r--], nums[i]);
            nums[i] = nums[r];
            nums[r--] = 2;
        }
    }
}
#3

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