Remove Duplicates from Sorted Array II

Follow up for "Remove Duplicates":
What if duplicates are allowed at mosttwice?

For example,
Given sorted arraynums=[1,1,1,2,2,3],

Your function should return length =5, with the first five elements ofnumsbeing1,1,2,2and3. It doesn't matter what you leave beyond the new length.

图解

分析

1. about special case, when nums.length small and equal to 2 , return nums.length, that is the minimum length this function could return
2. two pointers : slow and fast, initially to be 1
3. scan the array from index 2 to rightmost, using fast pointer, when nums[fast] is not equal to nums[fast-2], we assign nums[fast] to nums[slow] and increment slow

代码

class Solution {
     public int removeDuplicates(int[] nums) {

         if(nums.length<=2) return nums.length;

         int base = 2;
         for(int i = 2;i<nums.length;i++){
             if(nums[i]!=nums[base-2]){
                 nums[base]=nums[i];
                 base++;
             }
         }
         return base;

     }
}