public class Solution {

```
public void sortColors(int[] nums) {
if(nums == null) return ;
int zero = 0, second = nums.length - 1;
int cur = 0;
while(cur <= second) {
if(nums[cur] == 0) {
swap(nums, cur++, zero++);
} else if(nums[cur] == 1) {
cur++;
} else if(nums[cur] == 2) {
swap(nums, cur, second--);
}
}
}
private void swap(int []nums, int i, int j) {
int t = nums[i];
nums[i] = nums[j];
nums[j] = t;
}
```

}