解答1[Java]：

class Solution {
    public int removeDuplicates(int[] nums) {
        if(nums.length == 0) return 0;

        int head = 0;
        int tail = 0;
        for (;tail<nums.length;tail++){
            if(nums[head]!=nums[tail]){
                nums[++head]=nums[tail];
            }
        }

        return head+1;

    }
}