时间复杂度(O( n))
class Solution {
public:
int removeDuplicates(vector<int>& nums) {
if(nums.size()<=0)return 0;
int count = 0;
for(int i=1;i<nums.size();++i)
if(nums[i]!=nums[i-1])
nums[++count]=nums[i];
return count+1;
}
};